Add eslint-plugin-prettier and format all *_html.js

The only manual change needed to fix a test due to textContent match

Change-Id: Ic9e561f7d482e7a680b3c4bfe58decdbd5d4ec10
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.js b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.js
index 5fe516c..b5393ea 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-mode-selector/gr-diff-mode-selector_html.js
@@ -17,24 +17,38 @@
 import {html} from '@polymer/polymer/lib/utils/html-tag.js';
 
 export const htmlTemplate = html`
-    <style include="shared-styles">
-      :host {
-        /* Used to remove horizontal whitespace between the icons. */
-        display: flex;
-      }
-      gr-button.selected iron-icon {
-        color: var(--link-color);
-      }
-      iron-icon {
-        height: 1.3rem;
-        width: 1.3rem;
-      }
-    </style>
-    <gr-button id="sideBySideBtn" link="" has-tooltip="" class\$="[[_computeSelectedClass(mode, _VIEW_MODES.SIDE_BY_SIDE)]]" title="Side-by-side diff" on-click="_handleSideBySideTap">
-      <iron-icon icon="gr-icons:side-by-side"></iron-icon>
-    </gr-button>
-    <gr-button id="unifiedBtn" link="" has-tooltip="" title="Unified diff" class\$="[[_computeSelectedClass(mode, _VIEW_MODES.UNIFIED)]]" on-click="_handleUnifiedTap">
-      <iron-icon icon="gr-icons:unified"></iron-icon>
-    </gr-button>
-    <gr-rest-api-interface id="restAPI"></gr-rest-api-interface>
+  <style include="shared-styles">
+    :host {
+      /* Used to remove horizontal whitespace between the icons. */
+      display: flex;
+    }
+    gr-button.selected iron-icon {
+      color: var(--link-color);
+    }
+    iron-icon {
+      height: 1.3rem;
+      width: 1.3rem;
+    }
+  </style>
+  <gr-button
+    id="sideBySideBtn"
+    link=""
+    has-tooltip=""
+    class$="[[_computeSelectedClass(mode, _VIEW_MODES.SIDE_BY_SIDE)]]"
+    title="Side-by-side diff"
+    on-click="_handleSideBySideTap"
+  >
+    <iron-icon icon="gr-icons:side-by-side"></iron-icon>
+  </gr-button>
+  <gr-button
+    id="unifiedBtn"
+    link=""
+    has-tooltip=""
+    title="Unified diff"
+    class$="[[_computeSelectedClass(mode, _VIEW_MODES.UNIFIED)]]"
+    on-click="_handleUnifiedTap"
+  >
+    <iron-icon icon="gr-icons:unified"></iron-icon>
+  </gr-button>
+  <gr-rest-api-interface id="restAPI"></gr-rest-api-interface>
 `;