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

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

 // 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.
 
 #include "chrome/browser/ui/webui/media_router/media_router_dialog_controller_impl.h"
 
 #include <string>
 #include <vector>
 
 #include "base/trace_event/trace_event.h"
@@ skipping 179 matching lines @@
     MediaRouterUI* media_router_ui =
         static_cast<MediaRouterUI*>(web_ui->GetController());
     if (media_router_ui)
       media_router_ui->Close();
   }
 }
 
 void MediaRouterDialogControllerImpl::CreateMediaRouterDialog() {
   DCHECK(!dialog_observer_.get());
 
+  base::Time dialog_creation_time = base::Time::Now();
   TRACE_EVENT_NESTABLE_ASYNC_BEGIN0("media_router", "UI", initiator());
 
   Profile* profile =
       Profile::FromBrowserContext(initiator()->GetBrowserContext());
   DCHECK(profile);
 
   WebDialogDelegate* web_dialog_delegate =
       new MediaRouterDialogDelegate(action_);
   // |web_dialog_delegate|'s owner is |constrained_delegate|.
   // |constrained_delegate| is owned by the parent |views::View|.
@@ skipping 15 matching lines @@
   ConstrainedWebDialogDelegate* constrained_delegate =
       ShowConstrainedWebDialogWithAutoResize(
           profile, web_dialog_delegate, initiator(), min_size, max_size);
 #endif
 
   WebContents* media_router_dialog = constrained_delegate->GetWebContents();
   TRACE_EVENT_NESTABLE_ASYNC_INSTANT1("media_router", "UI", initiator(),
                                       "WebContents created",
                                       media_router_dialog);
 
+  // |media_router_ui| is created when |constrained_delegate| is created.
+  // For tests, GetWebUI() returns a nullptr.
+  if (media_router_dialog->GetWebUI()) {
+    MediaRouterUI* media_router_ui = static_cast<MediaRouterUI*>(
+        media_router_dialog->GetWebUI()->GetController());
+    DCHECK(media_router_ui);
+    media_router_ui->SetUIInitializationTimer(dialog_creation_time);
+  }
+
   media_router_dialog_pending_ = true;
 
   dialog_observer_.reset(new DialogWebContentsObserver(
       media_router_dialog, this));
 
   if (action_)
     action_->OnPopupShown();
 }
 
 void MediaRouterDialogControllerImpl::Reset() {
@@ skipping 43 matching lines @@
           ->GetWeakPtr();
   if (!create_connection_request.get()) {
     media_router_ui->InitWithDefaultMediaSource(delegate);
   } else {
     media_router_ui->InitWithPresentationSessionRequest(
         initiator(), delegate, create_connection_request.Pass());
   }
 }
 
 }  // namespace media_router