Desktop Aura: Allow tab drags out of window.

ui/aura/root_window_observer.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 UI_AURA_ROOT_WINDOW_OBSERVER_H_
 #define UI_AURA_ROOT_WINDOW_OBSERVER_H_
 
 #include "ui/aura/aura_export.h"
 
 namespace gfx {
+class Point;
 class Size;
 }
 
 namespace aura {
 class RootWindow;
 class Window;
 
 class AURA_EXPORT RootWindowObserver {
  public:
   // Invoked after the RootWindow is resized.
   virtual void OnRootWindowResized(const RootWindow* root,
                                    const gfx::Size& old_size) {}
 
+  // Invoked after the RootWindow has been moved on screen.
+  virtual void OnRootWindowMoved(const RootWindow* root,
+                                 const gfx::Point& new_origin) {}
+
   // Invoked when the native windowing system sends us a request to close our
   // window.
   virtual void OnRootWindowHostCloseRequested(const RootWindow* root) {}
 
   // Invoked when the keyboard mapping has changed.
   virtual void OnKeyboardMappingChanged(const RootWindow* root) {}
 
  protected:
   virtual ~RootWindowObserver() {}
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_ROOT_WINDOW_OBSERVER_H_