ui: Cleanup class/struct forward declarations

ui/wm/public/activation_client.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_WM_PUBLIC_ACTIVATION_CLIENT_H_
 #define UI_WM_PUBLIC_ACTIVATION_CLIENT_H_
 
 #include "ui/aura/aura_export.h"
 
-namespace ui {
-class Event;
-}
-
 namespace aura {
 class Window;
 
 namespace client {
 class ActivationChangeObserver;
 
 // An interface implemented by an object that manages window activation.
 class AURA_EXPORT ActivationClient {
  public:
   // Adds/Removes ActivationChangeObservers.
@@ skipping 40 matching lines @@
 // TODO(beng): currently the UI framework (views) implements the actual
 //             close-on-deactivate component of this feature but it should be
 //             possible to implement in the aura client.
 AURA_EXPORT void SetHideOnDeactivate(Window* window, bool hide_on_deactivate);
 AURA_EXPORT bool GetHideOnDeactivate(Window* window);
 
 }  // namespace clients
 }  // namespace aura
 
 #endif  // UI_WM_PUBLIC_ACTIVATION_CLIENT_H_