Observe for window's (self) deletion during activation/focus change

ui/aura/aura.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
@@ skipping 74 matching lines @@
         'root_window_host_win.h',
         'root_window_mac.h',
         'root_window_mac.mm',
         'root_window_view_mac.h',
         'root_window_view_mac.mm',
         'root_window.cc',
         'root_window.h',
         'window.cc',
         'window.h',
         'window_delegate.h',
+        'window_destruction_observer.cc',
+        'window_destruction_observer.h',
         'window_observer.h',
         'window_tracker.cc',
         'window_tracker.h',
       ],
       'conditions': [
         ['OS=="mac"', {
           'sources/': [
             ['exclude', 'client/dispatcher_client.cc'],
             ['exclude', 'client/dispatcher_client.h'],
           ],
@@ skipping 166 matching lines @@
         # osmesa GL implementation is used on linux.
         ['OS=="linux"', {
           'dependencies': [
             '<(DEPTH)/third_party/mesa/mesa.gyp:osmesa',
           ],
         }],
       ],
     },
   ],
 }