Make sure WindowObservers are removed from window before destruction

ash/drag_drop/drag_drop_controller.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/drag_drop/drag_drop_controller.h"
 
 #include "ash/drag_drop/drag_drop_tracker.h"
 #include "ash/drag_drop/drag_image_view.h"
 #include "ash/shell.h"
 #include "ash/wm/coordinate_conversion.h"
@@ skipping 443 matching lines @@
               static_cast<aura::Window*>(drag_source_window_)));
       DoDragCancel(kTouchCancelAnimationDuration);
       break;
     default:
       break;
   }
   event->SetHandled();
 }
 
 void DragDropController::OnWindowDestroyed(aura::Window* window) {
-  if (drag_window_ == window) {
-    drag_window_->RemoveObserver(this);
+  if (drag_window_ == window)
     drag_window_ = NULL;
-  }
-  if (drag_source_window_ == window) {
-    drag_source_window_->RemoveObserver(this);
+  if (drag_source_window_ == window)
     drag_source_window_ = NULL;
-  }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DragDropController, protected:
 
 gfx::LinearAnimation* DragDropController::CreateCancelAnimation(
     int duration,
     int frame_rate,
     gfx::AnimationDelegate* delegate) {
   return new gfx::LinearAnimation(duration, frame_rate, delegate);
@@ skipping 79 matching lines @@
     drag_window_->RemoveObserver(this);
   drag_window_ = NULL;
   drag_data_ = NULL;
   // Cleanup can be called again while deleting DragDropTracker, so use Pass
   // instead of reset to avoid double free.
   drag_drop_tracker_.Pass();
 }
 
 }  // namespace internal
 }  // namespace ash