Make UserActivityDetector a singleton

extensions/shell/browser/shell_desktop_controller.h

 // Copyright 2014 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 EXTENSIONS_SHELL_BROWSER_SHELL_DESKTOP_CONTROLLER_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_DESKTOP_CONTROLLER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 29 matching lines @@
 #if defined(OS_CHROMEOS)
 namespace ui {
 class UserActivityPowerManagerNotifier;
 }
 #endif
 
 namespace wm {
 class CompoundEventFilter;
 class CursorManager;
 class InputMethodEventFilter;
-class UserActivityDetector;
 }
 
 namespace extensions {
 class AppWindowClient;
 class Extension;
 
 // Handles desktop-related tasks for app_shell.
 class ShellDesktopController : public DesktopController,
                                public aura::client::WindowTreeClient,
 #if defined(OS_CHROMEOS)
@@ skipping 59 matching lines @@
   scoped_ptr<wm::CompoundEventFilter> root_window_event_filter_;
 
   scoped_ptr<aura::client::DefaultCaptureClient> capture_client_;
 
   scoped_ptr<wm::InputMethodEventFilter> input_method_filter_;
 
   scoped_ptr<aura::client::FocusClient> focus_client_;
 
   scoped_ptr<wm::CursorManager> cursor_manager_;
 
-  scoped_ptr<wm::UserActivityDetector> user_activity_detector_;
 #if defined(OS_CHROMEOS)
   scoped_ptr<ui::UserActivityPowerManagerNotifier> user_activity_notifier_;
 #endif
 
   scoped_ptr<AppWindowClient> app_window_client_;
 
   // NativeAppWindow::Close() deletes the AppWindow.
   std::vector<AppWindow*> app_windows_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellDesktopController);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_DESKTOP_CONTROLLER_H_