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

chrome/browser/resources/media_router/media_router_data.js

Index: chrome/browser/resources/media_router/media_router_data.js
diff --git a/chrome/browser/resources/media_router/media_router_data.js b/chrome/browser/resources/media_router/media_router_data.js
index d51414707a3a7ae97e83066681b3bc8e26dc39bd..37cc029c7bce7010dcff90e7654eb784554d9e42 100644
--- a/chrome/browser/resources/media_router/media_router_data.js
+++ b/chrome/browser/resources/media_router/media_router_data.js
@@ -104,10 +104,11 @@ cr.define('media_router', function() {
    * @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;
 
@@ -116,6 +117,9 @@ cr.define('media_router', function() {
 
     /** @type {?string} */
     this.host = host || null;
+
+    /** @type {boolean} */
+    this.isForced = isForced;
   };
 
   /**