[Media Router] Add UMA metrics to record the load time for route controls

chrome/browser/resources/media_router/media_router_browser_api.js

Index: chrome/browser/resources/media_router/media_router_browser_api.js
diff --git a/chrome/browser/resources/media_router/media_router_browser_api.js b/chrome/browser/resources/media_router/media_router_browser_api.js
index 482decffa92a71d194ed75ee775267081ec3a6fb..11a83f9cd3dbf48330d0e864f547beef2542136f 100644
--- a/chrome/browser/resources/media_router/media_router_browser_api.js
+++ b/chrome/browser/resources/media_router/media_router_browser_api.js
@@ -214,6 +214,16 @@ cr.define('media_router.browserApi', function() {
     chrome.send('reportTimeToInitialActionClose', [timeMs]);
   }
 
+  /**
+   * Reports the time, in ms, it took the WebUI route controller to load media
+   * status info.
+   *
+   * @param {number} timeMs
+   */
+  function reportWebUIRouteControllerLoaded(timeMs) {
+    chrome.send('reportWebUIRouteControllerLoaded', [timeMs]);
+  }
+
   /**
    * Requests data to initialize the WebUI with.
    * The data will be returned via media_router.ui.setInitialData.
@@ -309,6 +319,7 @@ cr.define('media_router.browserApi', function() {
     reportSinkCount: reportSinkCount,
     reportTimeToClickSink: reportTimeToClickSink,
     reportTimeToInitialActionClose: reportTimeToInitialActionClose,
+    reportWebUIRouteControllerLoaded: reportWebUIRouteControllerLoaded,
     requestInitialData: requestInitialData,
     requestRoute: requestRoute,
     searchSinksAndCreateRoute: searchSinksAndCreateRoute,