[Media Router] Add UMA metrics for Media Router Dialog WebUI performance.

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 51 matching lines @@
    *   castModes - list of available cast modes.
    *   initialCastModeType - cast mode to show initially. Expected to be
    *       included in |castModes|.
    */
   function setInitialData(data) {
     container.deviceMissingUrl = data['deviceMissingUrl'];
     container.allSinks = data['sinks'];
     container.routeList = data['routes'];
     container.initializeCastModes(data['castModes'],
         data['initialCastModeType']);
+    media_router.browserApi.onInitialDataReceived();
   }
 
   /**
    * Sets current issue to |issue|, or clears the current issue if |issue| is
    * null.
    *
    * @param {?media_router.Issue} issue
    */
   function setIssue(issue) {
     container.issue = issue;
@@ skipping 55 matching lines @@
   /**
    * Closes the given route.
    *
    * @param {!media_router.Route} route
    */
   function closeRoute(route) {
     chrome.send('closeRoute', [{routeId: route.id}]);
   }
 
   /**
+   * Indicates that the initial data has been received.
+   */
+  function onInitialDataReceived() {
+    chrome.send('onInitialDataReceived');
+  }
+
+  /**
    * Reports the current number of sinks.
    *
    * @param {number} sinkCount
    */
   function reportSinkCount(sinkCount) {
     chrome.send('reportSinkCount', [sinkCount]);
   }
 
   /**
    * Requests data to initialize the WebUI with.
@@ skipping 12 matching lines @@
    */
   function requestRoute(sinkId, selectedCastMode) {
     chrome.send('requestRoute',
                 [{sinkId: sinkId, selectedCastMode: selectedCastMode}]);
   }
 
   return {
     actOnIssue: actOnIssue,
     closeDialog: closeDialog,
     closeRoute: closeRoute,
+    onInitialDataReceived: onInitialDataReceived,
     reportSinkCount: reportSinkCount,
     requestInitialData: requestInitialData,
     requestRoute: requestRoute,
   };
 });