views: Extract Widget observer into its own header file.

ash/touch/touch_observer_hud.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 ASH_TOUCH_TOUCH_OBSERVER_HUD_H_
 #define ASH_TOUCH_TOUCH_OBSERVER_HUD_H_
 
 #include "ash/shell.h"
 #include "ui/aura/event_filter.h"
 #include "ui/gfx/point.h"
-#include "ui/views/widget/widget.h"
+#include "ui/views/widget/widget_observer.h"
 
 namespace aura {
 class MouseEvent;
 class KeyEvent;
 class Window;
 }
 
 namespace views {
 class Label;
 class Widget;
 }
 
 namespace ash {
 namespace internal {
 
 class TouchHudCanvas;
 
 // An event filter which handles system level gesture events.
 class TouchObserverHUD : public aura::EventFilter,
-                         public views::Widget::Observer {
+                         public views::WidgetObserver {
  public:
   TouchObserverHUD();
   virtual ~TouchObserverHUD();
 
  private:
   void UpdateTouchPointLabel(int index);
 
   // Overriden from aura::EventFilter:
   virtual bool PreHandleKeyEvent(aura::Window* target,
                                  aura::KeyEvent* event) OVERRIDE;
   virtual bool PreHandleMouseEvent(aura::Window* target,
                                    aura::MouseEvent* event) OVERRIDE;
   virtual ui::TouchStatus PreHandleTouchEvent(aura::Window* target,
                                               aura::TouchEvent* event) OVERRIDE;
   virtual ui::GestureStatus PreHandleGestureEvent(
       aura::Window* target,
       aura::GestureEvent* event) OVERRIDE;
 
-  // Overridden from views::Widget::Observer.
+  // Overridden from views::WidgetObserver:
   virtual void OnWidgetClosing(views::Widget* widget) OVERRIDE;
 
   static const int kMaxTouchPoints = 32;
 
   views::Widget* widget_;
   TouchHudCanvas* canvas_;
   views::Label* touch_labels_[kMaxTouchPoints];
   gfx::Point touch_positions_[kMaxTouchPoints];
   ui::EventType touch_status_[kMaxTouchPoints];
 
   DISALLOW_COPY_AND_ASSIGN(TouchObserverHUD);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_TOUCH_TOUCH_OBSERVER_HUD_H_