Added the Ash.Tab.TimeBetweenSwitchToExistingTabUserActions histogram to track time between tab swit

chrome/browser/ui/ash/chrome_shell_delegate.h

 // Copyright (c) 2012 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_UI_ASH_CHROME_SHELL_DELEGATE_H_
 #define CHROME_BROWSER_UI_ASH_CHROME_SHELL_DELEGATE_H_
 
 #include <string>
 
 #include "ash/shelf/shelf_item_types.h"
 #include "ash/shell_delegate.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
+#include "chrome/browser/ui/ash/metrics/user_metrics_recorder_proxy.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 class Browser;
 
 namespace ash {
 class ShelfItemDelegate;
 }
 
 namespace content {
@@ skipping 60 matching lines @@
   void PlatformInit();
 
   static ChromeShellDelegate* instance_;
 
   content::NotificationRegistrar registrar_;
 
   ChromeLauncherController* shelf_delegate_;
 
   ObserverList<ash::VirtualKeyboardStateObserver> keyboard_state_observer_list_;
 
+  // Proxy's events from chrome/browser to ash::UserMetricsRecorder.

[Alexei Svitkine (slow), 2015/05/15 19:19:56]

Nit: Proxies.

But actually, I don't see this class logging any user actions. Is the intention
for this to come in future CLs? Otherwise, it doesn't seem to be accurately
named.

[bruthig, 2015/05/15 19:36:21]

Fixed Proxy's to Proxies.

Summary of discussion offline.  UserMetricsRecorderProxy intentionally uses
'Metrics' as opposed to 'Actions' to hopefully include histograms as well.  The
actual recording is done by the ash::UserMetricsRecorder class.

+  scoped_ptr<ash::UserMetricsRecorderProxy> user_metrics_recorder_proxy_;
+
 #if defined(OS_CHROMEOS)
   scoped_ptr<chromeos::DisplayConfigurationObserver>
       display_configuration_observer_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(ChromeShellDelegate);
 };
 
 #endif  // CHROME_BROWSER_UI_ASH_CHROME_SHELL_DELEGATE_H_