Add setting to isolate zoom changes by default.

chrome/browser/resources/options/content_settings.js

 // Copyright (c) 2012 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.
 
 cr.exportPath('options');
 
 /**
  * @typedef {{appId: string,
  *            appName: (string|undefined),
  *            embeddingOrigin: (string|undefined),
@@ skipping 243 matching lines @@
    * Enables/disables the protected content exceptions button.
    * @param {boolean} enable Whether to enable the button.
    */
   ContentSettings.enableProtectedContentExceptions = function(enable) {
     var exceptionsButton = $('protected-content-exceptions');
     if (exceptionsButton)
       exceptionsButton.disabled = !enable;
   };
 
   /**
+   * Shows/hides the explanation of per-tab zoom scope under the list of any
+   * existing zoom level exceptions.
+   * @param {boolean} show Whether to show the explanation.
+   */
+  ContentSettings.showZoomScopeExplanation = function(show) {
+    $('zoom-levels-ignored-explanation').hidden = !show;
+  };
+
+  /**
    * Set the default microphone device based on the popup selection.
    * @private
    */
   ContentSettings.setDefaultMicrophone_ = function() {
     var deviceSelect = $('media-select-mic');
     chrome.send('setDefaultCaptureDevice', ['mic', deviceSelect.value]);
   };
 
   /**
    * Set the default camera device based on the popup selection.
    * @private
    */
   ContentSettings.setDefaultCamera_ = function() {
     var deviceSelect = $('media-select-camera');
     chrome.send('setDefaultCaptureDevice', ['camera', deviceSelect.value]);
   };
 
   // Export
   return {
     ContentSettings: ContentSettings
   };
 
 });