Make sure WindowObservers are removed from window before destruction

ui/aura/window.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_WINDOW_H_
 #define UI_AURA_WINDOW_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 570 matching lines @@
   void* user_data_;
 
   // Makes the window pass all events through to any windows behind it.
   bool ignore_events_;
 
   // See set_hit_test_outer_override().
   gfx::Insets hit_test_bounds_override_outer_mouse_;
   gfx::Insets hit_test_bounds_override_outer_touch_;
   gfx::Insets hit_test_bounds_override_inner_;
 
-  ObserverList<WindowObserver> observers_;
+  ObserverList<WindowObserver, true> observers_;
 
   // Value struct to keep the name and deallocator for this property.
   // Key cannot be used for this purpose because it can be char* or
   // WindowProperty<>.
   struct Value {
     const char* name;
     int64 value;
     PropertyDeallocator deallocator;
   };
 
   std::map<const void*, Value> prop_map_;
 
   DISALLOW_COPY_AND_ASSIGN(Window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_H_