Add support for MouseEnter/MouseExit event types to be sent to aura::Windows.

ui/aura/root_window.h

 // Copyright (c) 2011 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_ROOT_WINDOW_H_
 #define UI_AURA_ROOT_WINDOW_H_
 #pragma once
 
 #include "ui/aura/window.h"
 
@@ skipping 32 matching lines @@
   Window* mouse_pressed_handler() { return mouse_pressed_handler_; }
 
   // Overridden from Window:
   virtual FocusManager* GetFocusManager() OVERRIDE;
 
  protected:
   // Overridden from Window:
   virtual internal::RootWindow* GetRoot() OVERRIDE;
 
  private:
+  // Called whenever the mouse moves, tracks the current |mouse_moved_handler_|,
+  // sending exited and entered events as its value changes.
+  void HandleMouseMoved(const MouseEvent& event, Window* target);
+
   Window* mouse_pressed_handler_;
+  Window* mouse_moved_handler_;
   scoped_ptr<FocusManager> focus_manager_;
   Window* capture_window_;
 
   DISALLOW_COPY_AND_ASSIGN(RootWindow);
 };
 
 }  // namespace internal
 }  // namespace aura
 
 #endif  // UI_AURA_ROOT_WINDOW_H_