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

chrome/browser/media/router/media_router_metrics.h

 // 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.
 
 #ifndef CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_METRICS_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_METRICS_H_
 
+#include "base/time/time.h"
+
 namespace media_router {
 
 // NOTE: Do not renumber enums as that would confuse interpretation of
 // previously logged data. When making changes, also update the enum list
 // in tools/metrics/histograms/histograms.xml to keep it in sync.
 
 // Where the user clicked to open the Media Router dialog.
 enum class MediaRouterDialogOpenOrigin {
   TOOLBAR = 0,
   OVERFLOW_MENU = 1,
@@ skipping 27 matching lines @@
 
 class MediaRouterMetrics {
  public:
   // Records where the user clicked to open the Media Router dialog.
   static void RecordMediaRouterDialogOrigin(
       MediaRouterDialogOpenOrigin origin);
 
   // Records why the media route provider extension was woken up.
   static void RecordMediaRouteProviderWakeReason(
       MediaRouteProviderWakeReason reason);
+
+  // Records the duration it takes for the Media Router dialog to open and
+  // finish painting after a user clicks to open the dialog.
+  static void RecordMediaRouterDialogPaint(
+      const base::TimeDelta& delta);

[Ilya Sherman, 2015/12/10 04:48:55]

nit: I think that TimeDelta is typically passed by copy, since it's just an
int64.

[apacible, 2015/12/10 17:22:18]

Done.

+
+  // Records the duration it takes for the Media Router dialog to load its
+  // initial data after a user clicks to open the dialog.
+  static void RecordMediaRouterDialogLoaded(
+      const base::TimeDelta& delta);
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_METRICS_H_