[Media Router] Add P1 UMA metrics for Media Router.

chrome/browser/resources/media_router/media_router_ui_interface.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.
 
 // API invoked by the browser MediaRouterWebUIMessageHandler to communicate
 // with this UI.
 cr.define('media_router.ui', function() {
   'use strict';
 
   // The media-router-container element.
@@ skipping 126 matching lines @@
   /**
    * Closes the given route.
    *
    * @param {!media_router.Route} route
    */
   function closeRoute(route) {
     chrome.send('closeRoute', [{routeId: route.id}]);
   }
 
   /**
+   * Reports the current number of sinks.
+   *
+   * @param {number} sinkCount
+   */
+  function reportSinkCount(sinkCount) {
+    chrome.send('reportSinkCount', [{sinkCount: sinkCount}]);

[imcheng, 2015/10/26 17:18:14]

Is it possible to just return the sinkCount in the list without using object?

chrome.send('reportSinkCount', [sinkCount]);

[apacible, 2015/10/26 17:52:32]

Done.

+  }
+
+  /**
    * Requests data to initialize the WebUI with.
    * The data will be returned via media_router.ui.setInitialData.
    */
   function requestInitialData() {
     chrome.send('requestInitialData');
   }
 
   /**
    * Requests that a media route be started with the given sink.
    *
    * @param {string} sinkId The sink ID.
    * @param {number} selectedCastMode The value of the cast mode the user
    *   selected.
    */
   function requestRoute(sinkId, selectedCastMode) {
     chrome.send('requestRoute',
                 [{sinkId: sinkId, selectedCastMode: selectedCastMode}]);
   }
 
   return {
     actOnIssue: actOnIssue,
     closeDialog: closeDialog,
     closeRoute: closeRoute,
+    reportSinkCount: reportSinkCount,
     requestInitialData: requestInitialData,
     requestRoute: requestRoute,
   };
 });