Mojo: Cancel WaitingCallbacks when their HandleWrappers are closed.

mojo/mojo_base.gyp

 # Copyright 2014 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.
 
 # Essential components (and their tests) that are needed to build
 # Chrome should be here.  Other components that are useful only in
 # Mojo land like mojo_shell should be in mojo.gyp.
 {
   'includes': [
     'mojo_public.gypi',
@@ skipping 458 matching lines @@
         '../base/base.gyp:base',
         '../gin/gin.gyp:gin',
         'mojo_common_lib',
       ],
       'sources': [
         # Sources list duplicated in GN build.
         'bindings/js/core.cc',
         'bindings/js/core.h',
         'bindings/js/handle.cc',
         'bindings/js/handle.h',
+        'bindings/js/handle_close_observer.h',
         'bindings/js/support.cc',
         'bindings/js/support.h',
         'bindings/js/waiting_callback.cc',
         'bindings/js/waiting_callback.h',
       ],
     },
     {
       'target_name': 'mojo_message_generator',
       'type': 'executable',
       'dependencies': [
@@ skipping 124 matching lines @@
             'mojo_js_unittests.isolate',
           ],
           'sources': [
             'mojo_js_unittests.isolate',
           ],
         },
       ],
     }],
   ]
 }