[Media Router] Force DEFAULT cast mode when starting presentations from content.

chrome/browser/resources/media_router/media_router_data.js

 // Copyright 2015 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.
 
 // Any strings used here will already be localized. Values such as
 // CastMode.type or IDs will be defined elsewhere and determined later.
 
 cr.exportPath('media_router');
 
 /**
@@ skipping 86 matching lines @@
   REQUEST_PENDING: 'request_pending'
 };
 
 cr.define('media_router', function() {
   'use strict';
 
   /**
    * @param {number} type The type of cast mode.
    * @param {string} description The description of the cast mode.
    * @param {?string} host The hostname of the site to cast.
+   * @param {boolean} isForced True if the mode is forced.
    * @constructor
    * @struct
    */
-  var CastMode = function(type, description, host) {
+  var CastMode = function(type, description, host, isForced) {
     /** @type {number} */
     this.type = type;
 
     /** @type {string} */
     this.description = description;
 
     /** @type {?string} */
     this.host = host || null;
+
+    /** @type {boolean} */
+    this.isForced = isForced;
   };
 
   /**
    * Placeholder object for AUTO cast mode. See comment in CastModeType.
    * @const {!media_router.CastMode}
    */
   var AUTO_CAST_MODE = new CastMode(media_router.CastModeType.AUTO,
       loadTimeData.getString('autoCastMode'), null);
 
   /**
@@ skipping 134 matching lines @@
 
   return {
     AUTO_CAST_MODE: AUTO_CAST_MODE,
     CastMode: CastMode,
     Issue: Issue,
     Route: Route,
     Sink: Sink,
     TabInfo: TabInfo,
   };
 });