[MD settings] include source of policy for content settings

chrome/browser/resources/settings/site_settings/site_settings_prefs_browser_proxy.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 A helper object used from the "Site Settings" section to
  * interact with the content settings prefs.
  */
 
 /**
+ * The handler will send a police source that is similar, but not exactly the
+ * same as a ControlledBy value. If the ContentSettingProvider is omitted it
+ * should be treated as 'default'.
+ * @enum {string}
+ */
+var ContentSettingProvider = {
+  EXTENSION: 'extension',
+  PREFERENCE: 'preference',
+};
+
+/**
  * @typedef {{embeddingOrigin: string,
  *            embeddingDisplayName: string,
  *            incognito: boolean,
  *            origin: string,
  *            displayName: string,
  *            setting: string,
  *            source: string}}
  */
 var SiteException;
 
 /**
  * @typedef {{location: string,
  *            notifications: string}}
  */
 var CategoryDefaultsPref;
 
 /**
+ * @typedef {{setting: string,
+ *            source: ContentSettingProvider}}
+ */
+var DefaultContentSetting;
+
+/**
  * @typedef {{location: Array<SiteException>,
  *            notifications: Array<SiteException>}}
  */
 var ExceptionListPref;
 
 /**
  * @typedef {{defaults: CategoryDefaultsPref,
  *            exceptions: ExceptionListPref}}
  */
 var SiteSettingsPref;
@@ skipping 51 matching lines @@
     /**
      * Gets the cookie details for a particular site.
      * @param {string} site The name of the site.
      * @return {!Promise<!CookieDataSummaryItem>}
      */
     getCookieDetails: function(site) {},
 
     /**
      * Gets the default value for a site settings category.
      * @param {string} contentType The name of the category to query.
-     * @return {!Promise<string>} The string value of the default setting.
+     * @return {!Promise<!DefaultContentSetting>}
      */
     getDefaultValueForContentType: function(contentType) {},
 
     /**
      * Gets the exceptions (site list) for a particular category.
      * @param {string} contentType The name of the category to query.
      * @return {!Promise<!Array<!SiteException>>}
      */
     getExceptionList: function(contentType) {},
 
@@ skipping 270 matching lines @@
     removeZoomLevel: function(host) {
       chrome.send('removeZoomLevel', [host]);
     },
   };
 
   return {
     SiteSettingsPrefsBrowserProxy: SiteSettingsPrefsBrowserProxy,
     SiteSettingsPrefsBrowserProxyImpl: SiteSettingsPrefsBrowserProxyImpl,
   };
 });