Add setting to isolate zoom changes by default.

chrome/browser/resources/settings/site_settings/zoom_levels.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview
  * 'zoom-levels' is the polymer element for showing the sites that are zoomed in
- * or out.
+ * or out as well as the zoom scope setting.
  */
 
 Polymer({
   is: 'zoom-levels',
 
-  behaviors: [SiteSettingsBehavior, WebUIListenerBehavior],
+  behaviors: [I18nBehavior, SiteSettingsBehavior, WebUIListenerBehavior],
 
   properties: {
     /**
+     * Whether zoom changes are applied on a per-site basis or a per-tab basis.
+     * @type {boolean}
+     */
+    zoomScopeIsPerOrigin_: {
+      type: Boolean,
+      value: true,
+    },
+
+    /**
      * Array of sites that are zoomed in or out.
      * @type {!Array<ZoomLevelEntry>}
      */
     sites_: Array,
+
+    /** @private */
+    isGuest_: {
+      type: Boolean,
+      value: function() { return loadTimeData.getBoolean('isGuest'); }
+    },
   },
 
   ready: function() {
+    this.addWebUIListener('onZoomScopeChanged',
+        this.onZoomScopeChanged_.bind(this));
     this.addWebUIListener('onZoomLevelsChanged',
         this.onZoomLevelsChanged_.bind(this));
+    this.browserProxy.fetchZoomScope();
     this.browserProxy.fetchZoomLevels();
   },
 
   /**
+   * A handler for when the zoom scope changes.
+   * @param {boolean} zoomScopeIsPerOrigin The zoom scope setting.
+   */
+  onZoomScopeChanged_: function(zoomScopeIsPerOrigin) {
+    this.zoomScopeIsPerOrigin_ = zoomScopeIsPerOrigin;
+  },
+
+  /**
    * A handler for when zoom levels change.
    * @param {!Array<ZoomLevelEntry>} sites The up to date list of sites and
    *     their zoom levels.
    */
   onZoomLevelsChanged_: function(sites) {
     this.sites_ = sites;
   },
 
   /**
+   * Returns the label for the zoom scope toggle.
+   * @private
+   */
+  getScopeLabel_: function(zoomScopeIsPerOrigin) {
+    return zoomScopeIsPerOrigin ? this.i18n('siteSettingsZoomScopeOrigin')
+                                : this.i18n('siteSettingsZoomScopeTab');
+  },
+
+  /**
+   * Whether to show the text indicating that there are no zoomed sites.
+   * @private
+   */
+  showNoZoomedSites_: function(renderedCount, zoomScopeIsPerOrigin) {
+    return renderedCount == 0 && zoomScopeIsPerOrigin;
+  },
+
+  /**
+   * A handler for when the user toggles the zoom scope.
+   * @private
+   */
+  toggleZoomScope_: function() {
+    this.browserProxy.setZoomScopeIsPerOrigin(this.zoomScopeIsPerOrigin_);
+  },
+
+  /**
    * A handler for when a zoom level for a site is deleted.
    * @param {!{model: !{index: number}}} event
    * @private
    */
    removeZoomLevel_: function(event) {
      var site = this.sites_[event.model.index];
      this.browserProxy.removeZoomLevel(site.origin);
   },
 });