Fix Up SingletonHwnd Observer Lifetime Issues

ui/gfx/gfx.gyp

 # Copyright (c) 2013 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 290 matching lines @@
         'vsync_provider.h',
         'win/direct_write.cc',
         'win/direct_write.h',
         'win/dpi.cc',
         'win/dpi.h',
         'win/hwnd_util.cc',
         'win/hwnd_util.h',
         'win/scoped_set_map_mode.h',
         'win/singleton_hwnd.cc',
         'win/singleton_hwnd.h',
+        'win/singleton_hwnd_observer.cc',
+        'win/singleton_hwnd_observer.h',
         'win/window_impl.cc',
         'win/window_impl.h',
       ],
       'includes': [
         '../../build/android/increase_size_for_speed.gypi',
       ],
       'conditions': [
         ['OS=="ios"', {
           # Linkable dependents need to set the linker flag '-ObjC' in order to
           # use the categories in this target (e.g. NSString+CrStringDrawing.h).
@@ skipping 157 matching lines @@
          ],
          'variables': {
            'jni_gen_package': 'ui/gfx',
          },
          'includes': [ '../../build/jni_generator.gypi' ],
        },
      ],
     }],
   ],
 }