Moves maintaining ShellObservers back to Shell

ash/aura/wm_shell_aura.h

 // Copyright 2016 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 ASH_AURA_WM_SHELL_AURA_H_
 #define ASH_AURA_WM_SHELL_AURA_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 49 matching lines @@
       override;
   std::unique_ptr<wm::MaximizeModeEventHandler> CreateMaximizeModeEventHandler()
       override;
   std::unique_ptr<WorkspaceEventHandler> CreateWorkspaceEventHandler(
       WmWindow* workspace_window) override;
   std::unique_ptr<ScopedDisableInternalMouseAndKeyboard>
   CreateScopedDisableInternalMouseAndKeyboard() override;
   std::unique_ptr<ImmersiveFullscreenController>
   CreateImmersiveFullscreenController() override;
   std::unique_ptr<KeyEventWatcher> CreateKeyEventWatcher() override;
-  void OnOverviewModeStarting() override;
-  void OnOverviewModeEnded() override;
   SessionStateDelegate* GetSessionStateDelegate() override;
   void AddDisplayObserver(WmDisplayObserver* observer) override;
   void RemoveDisplayObserver(WmDisplayObserver* observer) override;
   void AddPointerWatcher(views::PointerWatcher* watcher,
                          views::PointerWatcherEventTypes events) override;
   void RemovePointerWatcher(views::PointerWatcher* watcher) override;
   bool IsTouchDown() override;
   void ToggleIgnoreExternalKeyboard() override;
   void SetLaserPointerEnabled(bool enabled) override;
   void SetPartialMagnifierEnabled(bool enabled) override;
@@ skipping 13 matching lines @@
 
   bool added_display_observer_ = false;
   base::ObserverList<WmDisplayObserver> display_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WmShellAura);
 };
 
 }  // namespace ash
 
 #endif  // ASH_AURA_WM_SHELL_AURA_H_