[MD settings] include source of policy for content settings

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

Index: chrome/browser/resources/settings/site_settings/site_settings_prefs_browser_proxy.js
diff --git a/chrome/browser/resources/settings/site_settings/site_settings_prefs_browser_proxy.js b/chrome/browser/resources/settings/site_settings/site_settings_prefs_browser_proxy.js
index 9c9345878edaf114f73ac85cd677f6d0d3d1ca22..b50e5369c1600258171553562ff9225e4a67b78c 100644
--- a/chrome/browser/resources/settings/site_settings/site_settings_prefs_browser_proxy.js
+++ b/chrome/browser/resources/settings/site_settings/site_settings_prefs_browser_proxy.js
@@ -8,6 +8,17 @@
  */
 
 /**
+ * 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,
@@ -25,6 +36,12 @@ var SiteException;
 var CategoryDefaultsPref;
 
 /**
+ * @typedef {{setting: string,
+ *            source: ContentSettingProvider}}
+ */
+var DefaultContentSetting;
+
+/**
  * @typedef {{location: Array<SiteException>,
  *            notifications: Array<SiteException>}}
  */
@@ -96,7 +113,7 @@ cr.define('settings', function() {
     /**
      * 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) {},