Move views::Accelerator to ui in order to use it from aura code.

views/controls/button/custom_button.h

Index: views/controls/button/custom_button.h
diff --git a/views/controls/button/custom_button.h b/views/controls/button/custom_button.h
index 29e96d47614b5cfbf72aeae32423821598acffae..ae6a8bf3f7ae34bea8046275d5183189e2b4a638 100644
--- a/views/controls/button/custom_button.h
+++ b/views/controls/button/custom_button.h
@@ -87,7 +87,7 @@ class VIEWS_EXPORT CustomButton : public Button,
   virtual void OnMouseMoved(const MouseEvent& event) OVERRIDE;
   virtual bool OnKeyPressed(const KeyEvent& event) OVERRIDE;
   virtual bool OnKeyReleased(const KeyEvent& event) OVERRIDE;
-  virtual bool AcceleratorPressed(const Accelerator& accelerator) OVERRIDE;
+  virtual bool AcceleratorPressed(const ui::Accelerator& accelerator) OVERRIDE;
   virtual void ShowContextMenu(const gfx::Point& p,
                                bool is_mouse_gesture) OVERRIDE;
   virtual void OnDragDone() OVERRIDE;