Attempt to re-land FocusManager removal from Aura.

ui/aura/focus_manager.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 UI_AURA_FOCUS_MANAGER_H_
-#define UI_AURA_FOCUS_MANAGER_H_
-
-#include "base/basictypes.h"
-#include "base/observer_list.h"
-#include "ui/aura/aura_export.h"
-#include "ui/aura/client/focus_client.h"
-
-namespace ui {
-class Event;
-}
-
-namespace aura {
-
-class Window;
-
-// An interface implemented by the Desktop to expose the focused window and
-// allow for it to be changed.
-class AURA_EXPORT FocusManager : public client::FocusClient {
- public:
-  FocusManager();
-  virtual ~FocusManager();
-
- private:
-  // Overridden from client::FocusClient:
-  virtual void AddObserver(client::FocusChangeObserver* observer) OVERRIDE;
-  virtual void RemoveObserver(client::FocusChangeObserver* observer) OVERRIDE;
-  virtual void FocusWindow(Window* window) OVERRIDE;
-  virtual void ResetFocusWithinActiveWindow(Window* window) OVERRIDE;
-  virtual Window* GetFocusedWindow() OVERRIDE;
-  virtual void OnWindowHiddenInRootWindow(aura::Window* window,
-                                          aura::RootWindow* root_window,
-                                          bool destroyed) OVERRIDE;
-
- protected:
-  aura::Window* focused_window_;
-
-  ObserverList<client::FocusChangeObserver> observers_;
-
-  DISALLOW_COPY_AND_ASSIGN(FocusManager);
-};
-
-}  // namespace aura
-
-#endif  // UI_AURA_FOCUS_MANAGER_H_