Fix copy & paste issue on diff list page

As multiple gr-diff on the list page, when process the selection,
should process the one with a valid selection.

Change-Id: Id8a3e05b7c898b7572b433f34c7bc1a38136f713

polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.js

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.js b/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.js
index 359a039..e46f959 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-selection/gr-diff-selection.js
@@ -192,15 +192,20 @@
       }
     }
 
-    /**
-     * For Polymer 2, use shadowRoot.getSelection instead.
-     */
     _getSelection() {
-      const diffHost = util.querySelector(document.body, 'gr-diff');
-      const selection = diffHost &&
-        diffHost.shadowRoot &&
-        diffHost.shadowRoot.getSelection();
-      return selection ? selection: window.getSelection();
+      const diffHosts = util.querySelectorAll(document.body, 'gr-diff');
+      if (!diffHosts.length) return window.getSelection();
+
+      const curDiffHost = diffHosts.find(diffHost => {
+        if (!diffHost || !diffHost.shadowRoot) return false;
+        const selection = diffHost.shadowRoot.getSelection();
+        // Pick the one with valid selection:
+        // https://developer.mozilla.org/en-US/docs/Web/API/Selection/type
+        return selection && selection.type !== 'None';
+      });
+
+      return curDiffHost ?
+        curDiffHost.shadowRoot.getSelection(): window.getSelection();
     }
 
     /**

polygerrit-ui/app/scripts/util.js

diff --git a/polygerrit-ui/app/scripts/util.js b/polygerrit-ui/app/scripts/util.js
index 672c43f..565b9b3 100644
--- a/polygerrit-ui/app/scripts/util.js
+++ b/polygerrit-ui/app/scripts/util.js
@@ -105,7 +105,7 @@
    */
   util.querySelector = (el, selector) => {
     let nodes = [el];
-    let element = null;
+    let result = null;
     while (nodes.length) {
       const node = nodes.pop();
 
@@ -113,19 +113,49 @@
       if (!node || !node.querySelector) continue;
 
       // Try find it with native querySelector directly
-      element = node.querySelector(selector);
+      result = node.querySelector(selector);
 
-      if (element) {
+      if (result) {
         break;
-      } else if (node.shadowRoot) {
-        // If shadowHost detected, add the host and its children
-        nodes = nodes.concat(Array.from(node.children));
-        nodes.push(node.shadowRoot);
-      } else {
-        nodes = nodes.concat(Array.from(node.children));
       }
+
+      // Add all nodes with shadowRoot and loop through
+      const allShadowNodes = [...node.querySelectorAll('*')]
+          .filter(child => !!child.shadowRoot)
+          .map(child => child.shadowRoot);
+      nodes = nodes.concat(allShadowNodes);
     }
-    return element;
+    return result;
+  };
+
+  /**
+   * Query selector all dom elements matching with certain selector.
+   *
+   * This is shadow DOM compatible, but only works when selector is within
+   * one shadow host, won't work if your selector is crossing
+   * multiple shadow hosts.
+   *
+   * Note: this can be very expensive, only use when have to.
+   */
+  util.querySelectorAll = (el, selector) => {
+    let nodes = [el];
+    const results = new Set();
+    while (nodes.length) {
+      const node = nodes.pop();
+
+      if (!node || !node.querySelectorAll) continue;
+
+      // Try find all from regular children
+      [...node.querySelectorAll(selector)]
+          .forEach(el => results.add(el));
+
+      // Add all nodes with shadowRoot and loop through
+      const allShadowNodes = [...node.querySelectorAll('*')]
+          .filter(child => !!child.shadowRoot)
+          .map(child => child.shadowRoot);
+      nodes = nodes.concat(allShadowNodes);
+    }
+    return [...results];
   };
 
   window.util = util;