Remove RootWindow reference from DragDropTracker. RootWindow reference in

ash/drag_drop/drag_drop_tracker.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_DRAG_DROP_DRAG_DROP_TRACKER_H_
 #define ASH_DRAG_DROP_DRAG_DROP_TRACKER_H_
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/base/events/event.h"
 
 namespace aura {
-class RootWindow;
 class Window;
 }
 
 namespace ash {
 namespace internal {
 
 // Provides functions for handling drag events inside and outside the root
 // window where drag is started. This internally sets up a capture window for
 // tracking drag events outside the root window where drag is initiated.
 // ash/wm/coordinate_conversion.h is used internally and only X11 environment
 // is supported for now.
 class ASH_EXPORT DragDropTracker {
  public:
-  explicit DragDropTracker(aura::RootWindow* root_window);
+  DragDropTracker();
   ~DragDropTracker();
 
-  // Gets the target located at |event| in the coordinates of the root window
-  // given to the constructor.
+  // Gets the target located at |event| in the coordinates of the active root
+  // window.
   aura::Window* GetTarget(const ui::LocatedEvent& event);
 
-  // Converts the locations of |event| in the coordinates of the root window
-  // given to the constructor to the ones in |target|'s coordinates.
+  // Converts the locations of |event| in the coordinates of the active root
+  // window to the ones in |target|'s coordinates.
   // Caller takes ownership of the returned object.
   ui::MouseEvent* ConvertMouseEvent(aura::Window* target,
                                     const ui::MouseEvent& event);
 
  private:
   // A window for capturing drag events while dragging.
   scoped_ptr<aura::Window> capture_window_;
 
   DISALLOW_COPY_AND_ASSIGN(DragDropTracker);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_DRAG_DROP_DRAG_DROP_TRACKER_H_