First shot at implementing drag&drop for Aura

ui/aura/desktop_delegate.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_DESKTOP_DELEGATE_H_
 #define UI_AURA_DESKTOP_DELEGATE_H_
 #pragma once
 
 #include "ui/aura/aura_export.h"
 
 namespace aura {
 
+class DragDropController;
 class Window;
 
 class AURA_EXPORT DesktopDelegate {
  public:
   virtual ~DesktopDelegate() {}
 
   // Called by the Window when its parent is set to NULL. The delegate is given
   // an opportunity to inspect the window and add it to a default parent window
   // of its choosing.
   virtual void AddChildToDefaultParent(Window* window) = 0;
 
   // Returns the window that should be activated other than |ignore|.
   virtual Window* GetTopmostWindowToActivate(Window* ignore) const = 0;
+
+  virtual DragDropController* GetDragDropController() const = 0;
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_DESKTOP_DELEGATE_H_