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

chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc

Index: chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
diff --git a/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc b/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
index dda4615c5e53206049a2792dd0d2162e0cf69349..c78ec1d38ced6f9d9e9af6afa49d3f33c9b10dba 100644
--- a/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
+++ b/chrome/browser/ui/webui/media_router/media_router_webui_message_handler.cc
@@ -60,6 +60,8 @@ const char kReportSelectedCastMode[] = "reportSelectedCastMode";
 const char kReportSinkCount[] = "reportSinkCount";
 const char kReportTimeToClickSink[] = "reportTimeToClickSink";
 const char kReportTimeToInitialActionClose[] = "reportTimeToInitialActionClose";
+const char kReportWebUIRouteControllerLoaded[] =
+    "reportWebUIRouteControllerLoaded";
 const char kSearchSinksAndCreateRoute[] = "searchSinksAndCreateRoute";
 const char kOnInitialDataReceived[] = "onInitialDataReceived";
 const char kOnMediaControllerAvailable[] = "onMediaControllerAvailable";
@@ -430,6 +432,11 @@ void MediaRouterWebUIMessageHandler::RegisterMessages() {
       base::Bind(
           &MediaRouterWebUIMessageHandler::OnReportTimeToInitialActionClose,
           base::Unretained(this)));
+  web_ui()->RegisterMessageCallback(
+      kReportWebUIRouteControllerLoaded,
+      base::Bind(
+          &MediaRouterWebUIMessageHandler::OnReportWebUIRouteControllerLoaded,
+          base::Unretained(this)));
   web_ui()->RegisterMessageCallback(
       kSearchSinksAndCreateRoute,
       base::Bind(&MediaRouterWebUIMessageHandler::OnSearchSinksAndCreateRoute,
@@ -808,6 +815,18 @@ void MediaRouterWebUIMessageHandler::OnReportTimeToClickSink(
                       base::TimeDelta::FromMillisecondsD(time_to_click));
 }
 
+void MediaRouterWebUIMessageHandler::OnReportWebUIRouteControllerLoaded(
+    const base::ListValue* args) {
+  DVLOG(1) << "OnReportWebUIRouteControllerLoaded";
+  double load_time;
+  if (!args->GetDouble(0, &load_time)) {
+    DVLOG(1) << "Unable to extract args.";
+    return;
+  }
+  UMA_HISTOGRAM_TIMES("MediaRouter.Ui.Dialog.LoadedWebUiRouteController",
+                      base::TimeDelta::FromMillisecondsD(load_time));
+}
+
 void MediaRouterWebUIMessageHandler::OnReportTimeToInitialActionClose(
     const base::ListValue* args) {
   DVLOG(1) << "OnReportTimeToInitialActionClose";