Fix crash if window is destroyed while dragging it.

ash/wm/default_window_resizer.cc

 // 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.
 
 #include "ash/wm/default_window_resizer.h"
 
 #include "ash/shell.h"
 #include "ash/wm/coordinate_conversion.h"
 #include "ash/wm/cursor_manager.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 63 matching lines @@
   details_.window->SetBounds(new_bounds);
 }
 
 void DefaultWindowResizer::RevertDrag() {
   if (!did_move_or_resize_)
     return;
 
   details_.window->SetBounds(details_.initial_bounds);
 }
 
+aura::Window* DefaultWindowResizer::GetTarget() {
+  return details_.window;
+}
+
 DefaultWindowResizer::DefaultWindowResizer(const Details& details)
     : details_(details),
       did_move_or_resize_(false) {
   DCHECK(details_.is_resizable);
   ash::Shell::GetInstance()->cursor_manager()->LockCursor();
 }
 
 }  // namespace aura