diff --git a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata-it_test.html b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata-it_test.html
index c5dba2f..86f8aaf 100644
--- a/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata-it_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata-it_test.html
@@ -106,7 +106,7 @@
 
     suite('with plugin style', () => {
       setup(done => {
-        Gerrit._resetPlugins();
+        Gerrit._testOnly_resetPlugins();
         const pluginHost = fixture('plugin-host');
         pluginHost.config = {
           plugin: {
diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog-it_test.html b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog-it_test.html
index 5e5a89e..45f718f 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog-it_test.html
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog-it_test.html
@@ -131,7 +131,7 @@
     });
 
     test('lgtm plugin', done => {
-      Gerrit._resetPlugins();
+      Gerrit._testOnly_resetPlugins();
       const pluginHost = fixture('plugin-host');
       pluginHost.config = {
         plugin: {
diff --git a/polygerrit-ui/app/elements/plugins/gr-endpoint-decorator/gr-endpoint-decorator_test.html b/polygerrit-ui/app/elements/plugins/gr-endpoint-decorator/gr-endpoint-decorator_test.html
index 0883707..994d666 100644
--- a/polygerrit-ui/app/elements/plugins/gr-endpoint-decorator/gr-endpoint-decorator_test.html
+++ b/polygerrit-ui/app/elements/plugins/gr-endpoint-decorator/gr-endpoint-decorator_test.html
@@ -58,7 +58,7 @@
       stub('gr-endpoint-decorator', {
         _import: sandbox.stub().returns(Promise.resolve()),
       });
-      Gerrit._resetPlugins();
+      Gerrit._testOnly_resetPlugins();
       container = fixture('basic');
       Gerrit.install(p => plugin = p, '0.1', 'http://some/plugin/url.html');
       // Decoration
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js
new file mode 100644
index 0000000..7e7e927
--- /dev/null
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils.js
@@ -0,0 +1,103 @@
+/**
+ * @license
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+(function(window) {
+  'use strict';
+
+  const PRELOADED_PROTOCOL = 'preloaded:';
+
+  let _restAPI;
+  function getRestAPI() {
+    if (!_restAPI) {
+      _restAPI = document.createElement('gr-rest-api-interface');
+    }
+    return _restAPI;
+  }
+
+  /**
+   * Retrieves the name of the plugin base on the url.
+   * @param {string|URL} url
+   */
+  function getPluginNameFromUrl(url) {
+    if (!(url instanceof URL)) {
+      try {
+        url = new URL(url);
+      } catch (e) {
+        console.warn(e);
+        return null;
+      }
+    }
+    if (url.protocol === PRELOADED_PROTOCOL) {
+      return url.pathname;
+    }
+    const base = Gerrit.BaseUrlBehavior.getBaseUrl();
+    const pathname = url.pathname.replace(base, '');
+    // Site theme is server from predefined path.
+    if (pathname === '/static/gerrit-theme.html') {
+      return 'gerrit-theme';
+    } else if (!pathname.startsWith('/plugins')) {
+      console.warn('Plugin not being loaded from /plugins base path:',
+          url.href, '— Unable to determine name.');
+      return null;
+    }
+
+    // Pathname should normally look like this:
+    // /plugins/PLUGINNAME/static/SCRIPTNAME.html
+    // Or, for app/samples:
+    // /plugins/PLUGINNAME.html
+    // TODO(taoalpha): guard with a regex
+    return pathname.split('/')[2].split('.')[0];
+  }
+
+  // TODO (taoalpha): to be deprecated.
+  function send(method, url, opt_callback, opt_payload) {
+    return getRestAPI().send(method, url, opt_payload).then(response => {
+      if (response.status < 200 || response.status >= 300) {
+        return response.text().then(text => {
+          if (text) {
+            return Promise.reject(text);
+          } else {
+            return Promise.reject(response.status);
+          }
+        });
+      } else {
+        return getRestAPI().getResponseObject(response);
+      }
+    }).then(response => {
+      if (opt_callback) {
+        opt_callback(response);
+      }
+      return response;
+    });
+  }
+
+
+  // TEST only methods / properties
+
+  function testOnly_resetInternalState() {
+    _restAPI = undefined;
+  }
+
+  window._apiUtils = {
+    getPluginNameFromUrl,
+    send,
+    getRestAPI,
+
+    // TEST only methods
+    testOnly_resetInternalState,
+  };
+})(window);
\ No newline at end of file
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html
new file mode 100644
index 0000000..c407aa8
--- /dev/null
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-api-utils_test.html
@@ -0,0 +1,78 @@
+<!DOCTYPE html>
+<!--
+@license
+Copyright (C) 2019 The Android Open Source Project
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+<meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1.0, user-scalable=yes">
+<title>gr-api-interface</title>
+<script src="/test/common-test-setup.js"></script>
+<script src="/bower_components/webcomponentsjs/custom-elements-es5-adapter.js"></script>
+
+<script src="/bower_components/webcomponentsjs/webcomponents-lite.js"></script>
+<script src="/bower_components/web-component-tester/browser.js"></script>
+<link rel="import" href="../../../test/common-test-setup.html"/>
+<link rel="import" href="gr-js-api-interface.html">
+
+<script>void(0);</script>
+
+<script>
+
+  const PRELOADED_PROTOCOL = 'preloaded:';
+
+  suite('gr-api-utils tests', () => {
+    suite('test getPluginNameFromUrl', () => {
+      const {getPluginNameFromUrl} = window._apiUtils;
+
+      test('with empty string', () => {
+        assert.equal(getPluginNameFromUrl(''), null);
+      });
+
+      test('with invalid url', () => {
+        assert.equal(getPluginNameFromUrl('test'), null);
+      });
+
+      test('with random invalid url', () => {
+        assert.equal(getPluginNameFromUrl('http://example.com'), null);
+        assert.equal(
+            getPluginNameFromUrl('http://example.com/static/a.html'),
+            null
+        );
+      });
+
+      test('with valid urls', () => {
+        assert.equal(
+            getPluginNameFromUrl('http://example.com/plugins/a.html'),
+            'a'
+        );
+        assert.equal(
+            getPluginNameFromUrl('http://example.com/plugins/a/static/t.html'),
+            'a'
+        );
+      });
+
+      test('with preloaded urls', () => {
+        assert.equal(getPluginNameFromUrl(`${PRELOADED_PROTOCOL}a`), 'a');
+      });
+
+      test('with gerrit-theme override', () => {
+        assert.equal(
+            getPluginNameFromUrl('http://example.com/static/gerrit-theme.html'),
+            'gerrit-theme'
+        );
+      });
+    });
+  });
+</script>
\ No newline at end of file
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api_test.html
index 30bd366..0131912 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-change-actions-js-api_test.html
@@ -54,7 +54,7 @@
 
     suite('early init', () => {
       setup(() => {
-        Gerrit._resetPlugins();
+        Gerrit._testOnly_resetPlugins();
         Gerrit.install(p => { plugin = p; }, '0.1',
             'http://test.com/plugins/testplugin/static/test.js');
         // Mimic all plugins loaded.
@@ -76,7 +76,7 @@
 
     suite('normal init', () => {
       setup(() => {
-        Gerrit._resetPlugins();
+        Gerrit._testOnly_resetPlugins();
         element = fixture('basic');
         sinon.stub(element, '_editStatusChanged');
         element.change = {};
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.js
new file mode 100644
index 0000000..a567700
--- /dev/null
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit.js
@@ -0,0 +1,290 @@
+/**
+ * @license
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+ /**
+  * This defines the Gerrit instance. All methods directly attached to Gerrit
+  * should be defined or linked here.
+  */
+
+(function(window) {
+  'use strict';
+
+  /**
+   * Hash of loaded and installed plugins, name to Plugin object.
+   */
+  const _plugins = {};
+
+  /**
+   * Array of plugin URLs to be loaded, name to url.
+   */
+  let _pluginsPending = {};
+
+  let _pluginsInstalled = [];
+
+  let _pluginsPendingCount = -1;
+
+  const UNKNOWN_PLUGIN = 'unknown';
+  const PRELOADED_PROTOCOL = 'preloaded:';
+
+  const PLUGIN_LOADING_TIMEOUT_MS = 10000;
+
+  let _reporting;
+  const getReporting = () => {
+    if (!_reporting) {
+      _reporting = document.createElement('gr-reporting');
+    }
+    return _reporting;
+  };
+
+  // Import utils methods
+  const {
+      getPluginNameFromUrl,
+      send,
+      getRestAPI,
+  } = window._apiUtils;
+
+  const API_VERSION = '0.1';
+
+  /**
+   * Trigger the preinstalls for bundled plugins.
+   * This needs to happen before Gerrit as plugin bundle overrides the Gerrit.
+   */
+  function flushPreinstalls() {
+    if (window.Gerrit.flushPreinstalls) {
+      window.Gerrit.flushPreinstalls();
+    }
+  }
+  flushPreinstalls();
+
+  window.Gerrit = window.Gerrit || {};
+  const Gerrit = window.Gerrit;
+
+  let _resolveAllPluginsLoaded = null;
+  let _allPluginsPromise = null;
+
+  Gerrit._endpoints = new GrPluginEndpoints();
+
+  // Provide reset plugins function to clear installed plugins between tests.
+  const app = document.querySelector('#app');
+  if (!app) {
+    // No gr-app found (running tests)
+    const {
+      testOnly_resetInternalState,
+    } = window._apiUtils;
+    Gerrit._testOnly_installPreloadedPlugins = installPreloadedPlugins;
+    Gerrit._testOnly_flushPreinstalls = flushPreinstalls;
+    Gerrit._testOnly_resetPlugins = () => {
+      _allPluginsPromise = null;
+      _pluginsInstalled = [];
+      _pluginsPending = {};
+      _pluginsPendingCount = -1;
+      _reporting = null;
+      _resolveAllPluginsLoaded = null;
+      testOnly_resetInternalState();
+      Gerrit._endpoints = new GrPluginEndpoints();
+      for (const k of Object.keys(_plugins)) {
+        delete _plugins[k];
+      }
+    };
+  }
+
+  /**
+   * @deprecated Use plugin.styles().css(rulesStr) instead. Please, consult
+   * the documentation how to replace it accordingly.
+   */
+  Gerrit.css = function(rulesStr) {
+    console.warn('Gerrit.css(rulesStr) is deprecated!',
+        'Use plugin.styles().css(rulesStr)');
+    if (!Gerrit._customStyleSheet) {
+      const styleEl = document.createElement('style');
+      document.head.appendChild(styleEl);
+      Gerrit._customStyleSheet = styleEl.sheet;
+    }
+
+    const name = '__pg_js_api_class_' +
+        Gerrit._customStyleSheet.cssRules.length;
+    Gerrit._customStyleSheet.insertRule('.' + name + '{' + rulesStr + '}', 0);
+    return name;
+  };
+
+  Gerrit.install = function(callback, opt_version, opt_src) {
+    // HTML import polyfill adds __importElement pointing to the import tag.
+    const script = document.currentScript &&
+        (document.currentScript.__importElement || document.currentScript);
+
+    let src = opt_src || (script && script.src);
+    if (!src || src.startsWith('data:')) {
+      src = script && script.baseURI;
+    }
+    const name = getPluginNameFromUrl(src);
+
+    if (opt_version && opt_version !== API_VERSION) {
+      Gerrit._pluginInstallError(`Plugin ${name} install error: only version ` +
+          API_VERSION + ' is supported in PolyGerrit. ' + opt_version +
+          ' was given.');
+      return;
+    }
+
+    const existingPlugin = _plugins[name];
+    const plugin = existingPlugin || new Plugin(src);
+    try {
+      callback(plugin);
+      if (name) {
+        _plugins[name] = plugin;
+      }
+      if (!existingPlugin) {
+        Gerrit._pluginInstalled(src);
+      }
+    } catch (e) {
+      Gerrit._pluginInstallError(`${e.name}: ${e.message}`);
+    }
+  };
+
+  Gerrit.getLoggedIn = function() {
+    console.warn('Gerrit.getLoggedIn() is deprecated! ' +
+        'Use plugin.restApi().getLoggedIn()');
+    return document.createElement('gr-rest-api-interface').getLoggedIn();
+  };
+
+  Gerrit.get = function(url, callback) {
+    console.warn('.get() is deprecated! Use plugin.restApi().get()');
+    send('GET', url, callback);
+  };
+
+  Gerrit.post = function(url, payload, callback) {
+    console.warn('.post() is deprecated! Use plugin.restApi().post()');
+    send('POST', url, callback, payload);
+  };
+
+  Gerrit.put = function(url, payload, callback) {
+    console.warn('.put() is deprecated! Use plugin.restApi().put()');
+    send('PUT', url, callback, payload);
+  };
+
+  Gerrit.delete = function(url, opt_callback) {
+    console.warn('.delete() is deprecated! Use plugin.restApi().delete()');
+    return getRestAPI().send('DELETE', url).then(response => {
+      if (response.status !== 204) {
+        return response.text().then(text => {
+          if (text) {
+            return Promise.reject(text);
+          } else {
+            return Promise.reject(response.status);
+          }
+        });
+      }
+      if (opt_callback) {
+        opt_callback(response);
+      }
+      return response;
+    });
+  };
+
+  Gerrit.awaitPluginsLoaded = function() {
+    if (!_allPluginsPromise) {
+      if (Gerrit._arePluginsLoaded()) {
+        _allPluginsPromise = Promise.resolve();
+      } else {
+        let timeoutId;
+        _allPluginsPromise =
+          Promise.race([
+            new Promise(resolve => _resolveAllPluginsLoaded = resolve),
+            new Promise(resolve => timeoutId = setTimeout(
+                Gerrit._pluginLoadingTimeout, PLUGIN_LOADING_TIMEOUT_MS)),
+          ]).then(() => clearTimeout(timeoutId));
+      }
+    }
+    return _allPluginsPromise;
+  };
+
+  Gerrit._pluginLoadingTimeout = function() {
+    console.error(`Failed to load plugins: ${Object.keys(_pluginsPending)}`);
+    Gerrit._setPluginsPending([]);
+  };
+
+  Gerrit._setPluginsPending = function(plugins) {
+    _pluginsPending = plugins.reduce((o, url) => {
+      // TODO(viktard): Remove guard (@see Issue 8962)
+      o[getPluginNameFromUrl(url) || UNKNOWN_PLUGIN] = url;
+      return o;
+    }, {});
+    Gerrit._setPluginsCount(Object.keys(_pluginsPending).length);
+  };
+
+  Gerrit._setPluginsCount = function(count) {
+    _pluginsPendingCount = count;
+    if (Gerrit._arePluginsLoaded()) {
+      getReporting().pluginsLoaded(_pluginsInstalled);
+      if (_resolveAllPluginsLoaded) {
+        _resolveAllPluginsLoaded();
+      }
+    }
+  };
+
+  Gerrit._pluginInstallError = function(message) {
+    document.dispatchEvent(new CustomEvent('show-alert', {
+      detail: {
+        message: `Plugin install error: ${message}`,
+      },
+    }));
+    console.info(`Plugin install error: ${message}`);
+    Gerrit._setPluginsCount(_pluginsPendingCount - 1);
+  };
+
+  Gerrit._pluginInstalled = function(url) {
+    const name = getPluginNameFromUrl(url) || UNKNOWN_PLUGIN;
+    if (!_pluginsPending[name]) {
+      console.warn(`Unexpected plugin ${name} installed from ${url}.`);
+    } else {
+      delete _pluginsPending[name];
+      _pluginsInstalled.push(name);
+      Gerrit._setPluginsCount(_pluginsPendingCount - 1);
+      getReporting().pluginLoaded(name);
+      console.log(`Plugin ${name} installed.`);
+    }
+  };
+
+  Gerrit._arePluginsLoaded = function() {
+    return _pluginsPendingCount === 0;
+  };
+
+  Gerrit._getPluginScreenName = function(pluginName, screenName) {
+    return `${pluginName}-screen-${screenName}`;
+  };
+
+  Gerrit._isPluginPreloaded = function(url) {
+    const name = getPluginNameFromUrl(url);
+    if (name && Gerrit._preloadedPlugins) {
+      return name in Gerrit._preloadedPlugins;
+    } else {
+      return false;
+    }
+  };
+
+  function installPreloadedPlugins() {
+    if (!Gerrit._preloadedPlugins) { return; }
+    for (const name in Gerrit._preloadedPlugins) {
+      if (!Gerrit._preloadedPlugins.hasOwnProperty(name)) { continue; }
+      const callback = Gerrit._preloadedPlugins[name];
+      Gerrit.install(callback, API_VERSION, PRELOADED_PROTOCOL + name);
+    }
+  }
+
+  // Preloaded plugins should be installed after Gerrit.install() is set,
+  // since plugin preloader substitutes Gerrit.install() temporarily.
+  installPreloadedPlugins();
+})(window);
\ No newline at end of file
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit_test.html
new file mode 100644
index 0000000..9a05454
--- /dev/null
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-gerrit_test.html
@@ -0,0 +1,188 @@
+<!DOCTYPE html>
+<!--
+@license
+Copyright (C) 2019 The Android Open Source Project
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+<meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1.0, user-scalable=yes">
+<title>gr-api-interface</title>
+<script src="/test/common-test-setup.js"></script>
+<script src="/bower_components/webcomponentsjs/custom-elements-es5-adapter.js"></script>
+
+<script src="/bower_components/webcomponentsjs/webcomponents-lite.js"></script>
+<script src="/bower_components/web-component-tester/browser.js"></script>
+<link rel="import" href="../../../test/common-test-setup.html"/>
+<link rel="import" href="gr-js-api-interface.html">
+
+<script>void(0);</script>
+
+<test-fixture id="basic">
+  <template>
+    <gr-js-api-interface></gr-js-api-interface>
+  </template>
+</test-fixture>
+
+<script>
+  suite('gr-gerrit tests', () => {
+    let element;
+    let plugin;
+    let sandbox;
+    let sendStub;
+
+    setup(() => {
+      sandbox = sinon.sandbox.create();
+      sendStub = sandbox.stub().returns(Promise.resolve({status: 200}));
+      stub('gr-rest-api-interface', {
+        getAccount() {
+          return Promise.resolve({name: 'Judy Hopps'});
+        },
+        send(...args) {
+          return sendStub(...args);
+        },
+      });
+      element = fixture('basic');
+      Gerrit.install(p => { plugin = p; }, '0.1',
+          'http://test.com/plugins/testplugin/static/test.js');
+      Gerrit._setPluginsPending([]);
+    });
+
+    teardown(() => {
+      sandbox.restore();
+      element._removeEventCallbacks();
+      plugin = null;
+    });
+
+    test('reuse plugin for install calls', () => {
+      let otherPlugin;
+      Gerrit.install(p => { otherPlugin = p; }, '0.1',
+          'http://test.com/plugins/testplugin/static/test.js');
+      assert.strictEqual(plugin, otherPlugin);
+    });
+
+    test('flushes preinstalls if provided', () => {
+      assert.doesNotThrow(() => {
+        Gerrit._testOnly_flushPreinstalls();
+      });
+      window.Gerrit.flushPreinstalls = sandbox.stub();
+      Gerrit._testOnly_flushPreinstalls();
+      assert.isTrue(window.Gerrit.flushPreinstalls.calledOnce);
+      delete window.Gerrit.flushPreinstalls;
+    });
+
+    test('versioning', () => {
+      const callback = sandbox.spy();
+      Gerrit.install(callback, '0.0pre-alpha');
+      assert(callback.notCalled);
+    });
+
+    test('_setPluginsCount', done => {
+      stub('gr-reporting', {
+        pluginsLoaded() {
+          done();
+        },
+      });
+      Gerrit._setPluginsCount(0);
+    });
+
+    test('_arePluginsLoaded', () => {
+      assert.isTrue(Gerrit._arePluginsLoaded());
+      Gerrit._setPluginsCount(1);
+      assert.isFalse(Gerrit._arePluginsLoaded());
+      Gerrit._setPluginsCount(0);
+      assert.isTrue(Gerrit._arePluginsLoaded());
+    });
+
+    test('_pluginInstalled', () => {
+      const pluginsLoadedStub = sandbox.stub();
+      stub('gr-reporting', {
+        pluginsLoaded: (...args) => pluginsLoadedStub(...args),
+      });
+      const plugins = [
+        'http://test.com/plugins/foo/static/test.js',
+        'http://test.com/plugins/bar/static/test.js',
+      ];
+      Gerrit._setPluginsPending(plugins);
+      Gerrit._pluginInstalled(plugins[0]);
+      Gerrit._pluginInstalled(plugins[1]);
+      assert.isTrue(pluginsLoadedStub.calledWithExactly(['foo', 'bar']));
+    });
+
+    test('install calls _pluginInstalled', () => {
+      sandbox.stub(Gerrit, '_pluginInstalled');
+      Gerrit.install(p => { plugin = p; }, '0.1',
+          'http://test.com/plugins/testplugin/static/test.js');
+
+      // testplugin has already been installed once (in setup).
+      assert.isFalse(Gerrit._pluginInstalled.called);
+
+      // testplugin2 plugin has not yet been installed.
+      Gerrit.install(p => { plugin = p; }, '0.1',
+          'http://test.com/plugins/testplugin2/static/test.js');
+      assert.isTrue(Gerrit._pluginInstalled.calledOnce);
+    });
+
+    test('plugin install errors mark plugins as loaded', () => {
+      Gerrit._setPluginsCount(1);
+      Gerrit.install(() => {}, '0.0pre-alpha');
+      return Gerrit.awaitPluginsLoaded();
+    });
+
+    test('multiple ui plugins per java plugin', () => {
+      const file1 = 'http://test.com/plugins/qaz/static/foo.nocache.js';
+      const file2 = 'http://test.com/plugins/qaz/static/bar.js';
+      Gerrit._setPluginsPending([file1, file2]);
+      Gerrit.install(() => {}, '0.1', file1);
+      Gerrit.install(() => {}, '0.1', file2);
+      return Gerrit.awaitPluginsLoaded();
+    });
+
+    test('plugin install errors shows toasts', () => {
+      const alertStub = sandbox.stub();
+      document.addEventListener('show-alert', alertStub);
+      Gerrit._setPluginsCount(1);
+      Gerrit.install(() => {}, '0.0pre-alpha');
+      return Gerrit.awaitPluginsLoaded().then(() => {
+        assert.isTrue(alertStub.calledOnce);
+      });
+    });
+
+    test('Gerrit._isPluginPreloaded', () => {
+      Gerrit._preloadedPlugins = {baz: ()=>{}};
+      assert.isFalse(Gerrit._isPluginPreloaded('plugins/foo/bar'));
+      assert.isFalse(Gerrit._isPluginPreloaded('http://a.com/42'));
+      assert.isTrue(Gerrit._isPluginPreloaded('preloaded:baz'));
+      Gerrit._preloadedPlugins = null;
+    });
+
+    test('preloaded plugins are installed', () => {
+      const installStub = sandbox.stub();
+      Gerrit._preloadedPlugins = {foo: installStub};
+      Gerrit._testOnly_installPreloadedPlugins();
+      assert.isTrue(installStub.called);
+      const pluginApi = installStub.lastCall.args[0];
+      assert.strictEqual(pluginApi.getPluginName(), 'foo');
+    });
+
+    test('installing preloaded plugin', () => {
+      let plugin;
+      window.ASSETS_PATH = 'http://blips.com/chitz';
+      Gerrit.install(p => { plugin = p; }, '0.1', 'preloaded:foo');
+      assert.strictEqual(plugin.getPluginName(), 'foo');
+      assert.strictEqual(plugin.url('/some/thing.html'),
+          'http://blips.com/chitz/plugins/foo/some/thing.html');
+      delete window.ASSETS_PATH;
+    });
+  });
+</script>
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.html
index e460660..7fa2250 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.html
@@ -31,6 +31,7 @@
 <link rel="import" href="../gr-rest-api-interface/gr-rest-api-interface.html">
 
 <dom-module id="gr-js-api-interface">
+  <script src="gr-api-utils.js"></script>
   <script src="gr-annotation-actions-context.js"></script>
   <script src="gr-annotation-actions-js-api.js"></script>
   <script src="gr-change-actions-js-api.js"></script>
@@ -40,4 +41,5 @@
   <script src="gr-plugin-action-context.js"></script>
   <script src="gr-plugin-rest-api.js"></script>
   <script src="gr-public-js-api.js"></script>
+  <script src="gr-gerrit.js"></script>
 </dom-module>
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
index c7e4f09..330310f 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
@@ -73,23 +73,6 @@
       plugin = null;
     });
 
-    test('reuse plugin for install calls', () => {
-      let otherPlugin;
-      Gerrit.install(p => { otherPlugin = p; }, '0.1',
-          'http://test.com/plugins/testplugin/static/test.js');
-      assert.strictEqual(plugin, otherPlugin);
-    });
-
-    test('flushes preinstalls if provided', () => {
-      assert.doesNotThrow(() => {
-        Gerrit._flushPreinstalls();
-      });
-      window.Gerrit.flushPreinstalls = sandbox.stub();
-      Gerrit._flushPreinstalls();
-      assert.isTrue(window.Gerrit.flushPreinstalls.calledOnce);
-      delete window.Gerrit.flushPreinstalls;
-    });
-
     test('url', () => {
       assert.equal(plugin.url(), 'http://test.com/plugins/testplugin/');
       assert.equal(plugin.url('/static/test.js'),
@@ -313,12 +296,6 @@
       element.handleEvent(element.EventType.HIGHLIGHTJS_LOADED, {hljs: testHljs});
     });
 
-    test('versioning', () => {
-      const callback = sandbox.spy();
-      Gerrit.install(callback, '0.0pre-alpha');
-      assert(callback.notCalled);
-    });
-
     test('getAccount', done => {
       plugin.restApi().getLoggedIn().then(loggedIn => {
         assert.isTrue(loggedIn);
@@ -326,77 +303,6 @@
       });
     });
 
-    test('_setPluginsCount', done => {
-      stub('gr-reporting', {
-        pluginsLoaded() {
-          done();
-        },
-      });
-      Gerrit._setPluginsCount(0);
-    });
-
-    test('_arePluginsLoaded', () => {
-      assert.isTrue(Gerrit._arePluginsLoaded());
-      Gerrit._setPluginsCount(1);
-      assert.isFalse(Gerrit._arePluginsLoaded());
-      Gerrit._setPluginsCount(0);
-      assert.isTrue(Gerrit._arePluginsLoaded());
-    });
-
-    test('_pluginInstalled', () => {
-      const pluginsLoadedStub = sandbox.stub();
-      stub('gr-reporting', {
-        pluginsLoaded: (...args) => pluginsLoadedStub(...args),
-      });
-      const plugins = [
-        'http://test.com/plugins/foo/static/test.js',
-        'http://test.com/plugins/bar/static/test.js',
-      ];
-      Gerrit._setPluginsPending(plugins);
-      Gerrit._pluginInstalled(plugins[0]);
-      Gerrit._pluginInstalled(plugins[1]);
-      assert.isTrue(pluginsLoadedStub.calledWithExactly(['foo', 'bar']));
-    });
-
-    test('install calls _pluginInstalled', () => {
-      sandbox.stub(Gerrit, '_pluginInstalled');
-      Gerrit.install(p => { plugin = p; }, '0.1',
-          'http://test.com/plugins/testplugin/static/test.js');
-
-      // testplugin has already been installed once (in setup).
-      assert.isFalse(Gerrit._pluginInstalled.called);
-
-      // testplugin2 plugin has not yet been installed.
-      Gerrit.install(p => { plugin = p; }, '0.1',
-          'http://test.com/plugins/testplugin2/static/test.js');
-      assert.isTrue(Gerrit._pluginInstalled.calledOnce);
-    });
-
-    test('plugin install errors mark plugins as loaded', () => {
-      Gerrit._setPluginsCount(1);
-      Gerrit.install(() => {}, '0.0pre-alpha');
-      return Gerrit.awaitPluginsLoaded();
-    });
-
-    test('multiple ui plugins per java plugin', () => {
-      const file1 = 'http://test.com/plugins/qaz/static/foo.nocache.js';
-      const file2 = 'http://test.com/plugins/qaz/static/bar.js';
-      Gerrit._setPluginsPending([file1, file2]);
-      Gerrit.install(() => {}, '0.1', file1);
-      Gerrit.install(() => {}, '0.1', file2);
-      return Gerrit.awaitPluginsLoaded();
-    });
-
-    test('plugin install errors shows toasts', () => {
-      const alertStub = sandbox.stub();
-      document.addEventListener('show-alert', alertStub);
-      Gerrit._setPluginsCount(1);
-      Gerrit.install(() => {}, '0.0pre-alpha');
-      return Gerrit.awaitPluginsLoaded().then(() => {
-        assert.isTrue(alertStub.calledOnce);
-      });
-    });
-
     test('attributeHelper', () => {
       assert.isOk(plugin.attributeHelper());
     });
@@ -422,33 +328,6 @@
           element.EventType.ADMIN_MENU_LINKS);
     });
 
-    test('Gerrit._isPluginPreloaded', () => {
-      Gerrit._preloadedPlugins = {baz: ()=>{}};
-      assert.isFalse(Gerrit._isPluginPreloaded('plugins/foo/bar'));
-      assert.isFalse(Gerrit._isPluginPreloaded('http://a.com/42'));
-      assert.isTrue(Gerrit._isPluginPreloaded('preloaded:baz'));
-      Gerrit._preloadedPlugins = null;
-    });
-
-    test('preloaded plugins are installed', () => {
-      const installStub = sandbox.stub();
-      Gerrit._preloadedPlugins = {foo: installStub};
-      Gerrit._installPreloadedPlugins();
-      assert.isTrue(installStub.called);
-      const pluginApi = installStub.lastCall.args[0];
-      assert.strictEqual(pluginApi.getPluginName(), 'foo');
-    });
-
-    test('installing preloaded plugin', () => {
-      let plugin;
-      window.ASSETS_PATH = 'http://blips.com/chitz';
-      Gerrit.install(p => { plugin = p; }, '0.1', 'preloaded:foo');
-      assert.strictEqual(plugin.getPluginName(), 'foo');
-      assert.strictEqual(plugin.url('/some/thing.html'),
-          'http://blips.com/chitz/plugins/foo/some/thing.html');
-      delete window.ASSETS_PATH;
-    });
-
     suite('test plugin with base url', () => {
       let baseUrlPlugin;
 
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
index 3b7b80d..d44acea 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js
@@ -17,71 +17,18 @@
 (function(window) {
   'use strict';
 
-  /**
-   * Hash of loaded and installed plugins, name to Plugin object.
-   */
-  const _plugins = {};
-
-  /**
-   * Array of plugin URLs to be loaded, name to url.
-   */
-  let _pluginsPending = {};
-
-  let _pluginsInstalled = [];
-
-  let _pluginsPendingCount = -1;
-
   const PRELOADED_PROTOCOL = 'preloaded:';
 
-  const UNKNOWN_PLUGIN = 'unknown';
-
   const PANEL_ENDPOINTS_MAPPING = {
     CHANGE_SCREEN_BELOW_COMMIT_INFO_BLOCK: 'change-view-integration',
     CHANGE_SCREEN_BELOW_CHANGE_INFO_BLOCK: 'change-metadata-item',
   };
 
-  const PLUGIN_LOADING_TIMEOUT_MS = 10000;
-
-  let _restAPI;
-
-  const getRestAPI = () => {
-    if (!_restAPI) {
-      _restAPI = document.createElement('gr-rest-api-interface');
-    }
-    return _restAPI;
-  };
-
-  let _reporting;
-  const getReporting = () => {
-    if (!_reporting) {
-      _reporting = document.createElement('gr-reporting');
-    }
-    return _reporting;
-  };
-
-  // TODO (viktard): deprecate in favor of GrPluginRestApi.
-  function send(method, url, opt_callback, opt_payload) {
-    return getRestAPI().send(method, url, opt_payload).then(response => {
-      if (response.status < 200 || response.status >= 300) {
-        return response.text().then(text => {
-          if (text) {
-            return Promise.reject(text);
-          } else {
-            return Promise.reject(response.status);
-          }
-        });
-      } else {
-        return getRestAPI().getResponseObject(response);
-      }
-    }).then(response => {
-      if (opt_callback) {
-        opt_callback(response);
-      }
-      return response;
-    });
-  }
-
-  const API_VERSION = '0.1';
+  // Import utils methods
+  const {
+      getPluginNameFromUrl,
+      send,
+  } = window._apiUtils;
 
   /**
    * Plugin-provided custom components can affect content in extension
@@ -99,50 +46,6 @@
     STYLE: 'style',
   };
 
-  function flushPreinstalls() {
-    if (window.Gerrit.flushPreinstalls) {
-      window.Gerrit.flushPreinstalls();
-    }
-  }
-
-  function installPreloadedPlugins() {
-    if (!Gerrit._preloadedPlugins) { return; }
-    for (const name in Gerrit._preloadedPlugins) {
-      if (!Gerrit._preloadedPlugins.hasOwnProperty(name)) { continue; }
-      const callback = Gerrit._preloadedPlugins[name];
-      Gerrit.install(callback, API_VERSION, PRELOADED_PROTOCOL + name);
-    }
-  }
-
-  function getPluginNameFromUrl(url) {
-    if (!(url instanceof URL)) {
-      try {
-        url = new URL(url);
-      } catch (e) {
-        console.warn(e);
-        return null;
-      }
-    }
-    if (url.protocol === PRELOADED_PROTOCOL) {
-      return url.pathname;
-    }
-    const base = Gerrit.BaseUrlBehavior.getBaseUrl();
-    const pathname = url.pathname.replace(base, '');
-    // Site theme is server from predefined path.
-    if (pathname === '/static/gerrit-theme.html') {
-      return 'gerrit-theme';
-    } else if (!pathname.startsWith('/plugins')) {
-      console.warn('Plugin not being loaded from /plugins base path:',
-          url.href, '— Unable to determine name.');
-      return;
-    }
-    // Pathname should normally look like this:
-    // /plugins/PLUGINNAME/static/SCRIPTNAME.html
-    // Or, for app/samples:
-    // /plugins/PLUGINNAME.html
-    return pathname.split('/')[2].split('.')[0];
-  }
-
   function Plugin(opt_url) {
     this._domHooks = new GrDomHooksManager(this);
 
@@ -475,211 +378,5 @@
     },
   };
 
-  flushPreinstalls();
-
-  window.Gerrit = window.Gerrit || {};
-  const Gerrit = window.Gerrit;
-
-  let _resolveAllPluginsLoaded = null;
-  let _allPluginsPromise = null;
-
-  Gerrit._endpoints = new GrPluginEndpoints();
-
-  // Provide reset plugins function to clear installed plugins between tests.
-  const app = document.querySelector('#app');
-  if (!app) {
-    // No gr-app found (running tests)
-    Gerrit._installPreloadedPlugins = installPreloadedPlugins;
-    Gerrit._flushPreinstalls = flushPreinstalls;
-    Gerrit._resetPlugins = () => {
-      _allPluginsPromise = null;
-      _pluginsInstalled = [];
-      _pluginsPending = {};
-      _pluginsPendingCount = -1;
-      _reporting = null;
-      _resolveAllPluginsLoaded = null;
-      _restAPI = null;
-      Gerrit._endpoints = new GrPluginEndpoints();
-      for (const k of Object.keys(_plugins)) {
-        delete _plugins[k];
-      }
-    };
-  }
-
-  /**
-   * @deprecated Use plugin.styles().css(rulesStr) instead. Please, consult
-   * the documentation how to replace it accordingly.
-   */
-  Gerrit.css = function(rulesStr) {
-    console.warn('Gerrit.css(rulesStr) is deprecated!',
-        'Use plugin.styles().css(rulesStr)');
-    if (!Gerrit._customStyleSheet) {
-      const styleEl = document.createElement('style');
-      document.head.appendChild(styleEl);
-      Gerrit._customStyleSheet = styleEl.sheet;
-    }
-
-    const name = '__pg_js_api_class_' +
-        Gerrit._customStyleSheet.cssRules.length;
-    Gerrit._customStyleSheet.insertRule('.' + name + '{' + rulesStr + '}', 0);
-    return name;
-  };
-
-  Gerrit.install = function(callback, opt_version, opt_src) {
-    // HTML import polyfill adds __importElement pointing to the import tag.
-    const script = document.currentScript &&
-        (document.currentScript.__importElement || document.currentScript);
-
-    let src = opt_src || (script && script.src);
-    if (!src || src.startsWith('data:')) {
-      src = script && script.baseURI;
-    }
-    const name = getPluginNameFromUrl(src);
-
-    if (opt_version && opt_version !== API_VERSION) {
-      Gerrit._pluginInstallError(`Plugin ${name} install error: only version ` +
-          API_VERSION + ' is supported in PolyGerrit. ' + opt_version +
-          ' was given.');
-      return;
-    }
-
-    const existingPlugin = _plugins[name];
-    const plugin = existingPlugin || new Plugin(src);
-    try {
-      callback(plugin);
-      if (name) {
-        _plugins[name] = plugin;
-      }
-      if (!existingPlugin) {
-        Gerrit._pluginInstalled(src);
-      }
-    } catch (e) {
-      Gerrit._pluginInstallError(`${e.name}: ${e.message}`);
-    }
-  };
-
-  Gerrit.getLoggedIn = function() {
-    console.warn('Gerrit.getLoggedIn() is deprecated! ' +
-        'Use plugin.restApi().getLoggedIn()');
-    return document.createElement('gr-rest-api-interface').getLoggedIn();
-  };
-
-  Gerrit.get = function(url, callback) {
-    console.warn('.get() is deprecated! Use plugin.restApi().get()');
-    send('GET', url, callback);
-  };
-
-  Gerrit.post = function(url, payload, callback) {
-    console.warn('.post() is deprecated! Use plugin.restApi().post()');
-    send('POST', url, callback, payload);
-  };
-
-  Gerrit.put = function(url, payload, callback) {
-    console.warn('.put() is deprecated! Use plugin.restApi().put()');
-    send('PUT', url, callback, payload);
-  };
-
-  Gerrit.delete = function(url, opt_callback) {
-    console.warn('.delete() is deprecated! Use plugin.restApi().delete()');
-    return getRestAPI().send('DELETE', url).then(response => {
-      if (response.status !== 204) {
-        return response.text().then(text => {
-          if (text) {
-            return Promise.reject(text);
-          } else {
-            return Promise.reject(response.status);
-          }
-        });
-      }
-      if (opt_callback) {
-        opt_callback(response);
-      }
-      return response;
-    });
-  };
-
-  Gerrit.awaitPluginsLoaded = function() {
-    if (!_allPluginsPromise) {
-      if (Gerrit._arePluginsLoaded()) {
-        _allPluginsPromise = Promise.resolve();
-      } else {
-        let timeoutId;
-        _allPluginsPromise =
-          Promise.race([
-            new Promise(resolve => _resolveAllPluginsLoaded = resolve),
-            new Promise(resolve => timeoutId = setTimeout(
-                Gerrit._pluginLoadingTimeout, PLUGIN_LOADING_TIMEOUT_MS)),
-          ]).then(() => clearTimeout(timeoutId));
-      }
-    }
-    return _allPluginsPromise;
-  };
-
-  Gerrit._pluginLoadingTimeout = function() {
-    console.error(`Failed to load plugins: ${Object.keys(_pluginsPending)}`);
-    Gerrit._setPluginsPending([]);
-  };
-
-  Gerrit._setPluginsPending = function(plugins) {
-    _pluginsPending = plugins.reduce((o, url) => {
-      // TODO(viktard): Remove guard (@see Issue 8962)
-      o[getPluginNameFromUrl(url) || UNKNOWN_PLUGIN] = url;
-      return o;
-    }, {});
-    Gerrit._setPluginsCount(Object.keys(_pluginsPending).length);
-  };
-
-  Gerrit._setPluginsCount = function(count) {
-    _pluginsPendingCount = count;
-    if (Gerrit._arePluginsLoaded()) {
-      getReporting().pluginsLoaded(_pluginsInstalled);
-      if (_resolveAllPluginsLoaded) {
-        _resolveAllPluginsLoaded();
-      }
-    }
-  };
-
-  Gerrit._pluginInstallError = function(message) {
-    document.dispatchEvent(new CustomEvent('show-alert', {
-      detail: {
-        message: `Plugin install error: ${message}`,
-      },
-    }));
-    console.info(`Plugin install error: ${message}`);
-    Gerrit._setPluginsCount(_pluginsPendingCount - 1);
-  };
-
-  Gerrit._pluginInstalled = function(url) {
-    const name = getPluginNameFromUrl(url) || UNKNOWN_PLUGIN;
-    if (!_pluginsPending[name]) {
-      console.warn(`Unexpected plugin ${name} installed from ${url}.`);
-    } else {
-      delete _pluginsPending[name];
-      _pluginsInstalled.push(name);
-      Gerrit._setPluginsCount(_pluginsPendingCount - 1);
-      getReporting().pluginLoaded(name);
-      console.log(`Plugin ${name} installed.`);
-    }
-  };
-
-  Gerrit._arePluginsLoaded = function() {
-    return _pluginsPendingCount === 0;
-  };
-
-  Gerrit._getPluginScreenName = function(pluginName, screenName) {
-    return `${pluginName}-screen-${screenName}`;
-  };
-
-  Gerrit._isPluginPreloaded = function(url) {
-    const name = getPluginNameFromUrl(url);
-    if (name && Gerrit._preloadedPlugins) {
-      return name in Gerrit._preloadedPlugins;
-    } else {
-      return false;
-    }
-  };
-
-  // Preloaded plugins should be installed after Gerrit.install() is set,
-  // since plugin preloader substitutes Gerrit.install() temporarily.
-  installPreloadedPlugins();
+  window.Plugin = Plugin;
 })(window);
diff --git a/polygerrit-ui/app/test/common-test-setup.html b/polygerrit-ui/app/test/common-test-setup.html
index 696f6a5..c1d8bbd 100644
--- a/polygerrit-ui/app/test/common-test-setup.html
+++ b/polygerrit-ui/app/test/common-test-setup.html
@@ -53,8 +53,8 @@
   (function() {
     setup(() => {
       if (!window.Gerrit) { return; }
-      if (Gerrit._resetPlugins) {
-        Gerrit._resetPlugins();
+      if (Gerrit._testOnly_resetPlugins) {
+        Gerrit._testOnly_resetPlugins();
       }
     });
   })();
diff --git a/polygerrit-ui/app/test/index.html b/polygerrit-ui/app/test/index.html
index 10d5aff..a0e85ef 100644
--- a/polygerrit-ui/app/test/index.html
+++ b/polygerrit-ui/app/test/index.html
@@ -188,7 +188,9 @@
     'shared/gr-js-api-interface/gr-annotation-actions-js-api_test.html',
     'shared/gr-js-api-interface/gr-change-actions-js-api_test.html',
     'shared/gr-js-api-interface/gr-change-reply-js-api_test.html',
+    'shared/gr-js-api-interface/gr-api-utils_test.html',
     'shared/gr-js-api-interface/gr-js-api-interface_test.html',
+    'shared/gr-js-api-interface/gr-gerrit_test.html',
     // TODO: uncomment file & fix tests. The file was missed in this list for a long time.
     // 'shared/gr-js-api-interface/gr-plugin-action-context_test.html',
     'shared/gr-js-api-interface/gr-plugin-endpoints_test.html',