[MD setting] tool tips on controlledBy site exceptions

chrome/test/data/webui/settings/test_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.
 
 /**
+ * Only used for tests.
+ * @typedef {{
+ *   auto_downloads: !Array<!RawSiteException>},
+ *   background_sync: !Array<!RawSiteException>},
+ *   camera: !Array<!RawSiteException>},
+ *   cookies: !Array<!RawSiteException>},
+ *   geolocation: !Array<!RawSiteException>},
+ *   javascript: !Array<!RawSiteException>},
+ *   mic: !Array<!RawSiteException>},
+ *   midiDevices: !Array<!RawSiteException>},
+ *   notifications: !Array<!RawSiteException>},
+ *   plugins: !Array<!RawSiteException>},
+ *   popups: !Array<!RawSiteException>},
+ *   unsandboxed_plugins: !Array<!RawSiteException>},
+ * }}
+ */
+var ExceptionListPref;
+
+/**
+ * In the real (non-test) code, these data come from the C++ handler.
+ * Only used for tests.
+ * @typedef {{defaults: CategoryDefaultsPref,
+ *            exceptions: ExceptionListPref}}
+ */
+var SiteSettingsPref;
+
+/**
  * An example empty pref.
  * @type {SiteSettingsPref}
  */
 var prefsEmpty = {
   defaults: {
     auto_downloads: '',
     background_sync: '',
     camera: '',
     cookies: '',
     geolocation: '',
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   /** @override */
   setProtocolDefault: function() {
     this.methodCalled('setProtocolDefault', arguments);
   },
 
   /** @override */
   removeProtocolHandler: function() {
     this.methodCalled('removeProtocolHandler', arguments);
   }
 };