Make sure WindowObservers are removed from window before destruction

ash/wm/window_cycle_list.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/window_cycle_list.h"
 
 #include "ash/shell.h"
 #include "ash/wm/mru_window_tracker.h"
 #include "ash/wm/window_util.h"
 #include "ui/aura/window.h"
@@ skipping 54 matching lines @@
 
 int WindowCycleList::GetWindowIndex(aura::Window* window) {
   WindowList::const_iterator it =
       std::find(windows_.begin(), windows_.end(), window);
   if (it == windows_.end())
     return -1;  // Not found.
   return it - windows_.begin();
 }
 
 void WindowCycleList::OnWindowDestroyed(aura::Window* window) {
-  window->RemoveObserver(this);
-
   WindowList::iterator i = std::find(windows_.begin(), windows_.end(), window);
   DCHECK(i != windows_.end());
   int removed_index = static_cast<int>(i - windows_.begin());
   windows_.erase(i);
   if (current_index_ > removed_index)
     current_index_--;
   else if (current_index_ == static_cast<int>(windows_.size()))
     current_index_--;
 }
 
 }  // namespace ash