Allow synchronous messages to be sent from threads other than the main thread...

ipc/ipc.gypi

 # Copyright (c) 2009 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.
 
 {
   'target_defaults': {
     'variables': {
       'ipc_target': 0,
     },
     'target_conditions': [
@@ skipping 18 matching lines @@
           'ipc_message_macros.h',
           'ipc_message_utils.cc',
           'ipc_message_utils.h',
           'ipc_platform_file.h',
           'ipc_switches.cc',
           'ipc_switches.h',
           'ipc_sync_channel.cc',
           'ipc_sync_channel.h',
           'ipc_sync_message.cc',
           'ipc_sync_message.h',
+          'ipc_sync_message_filter.cc',
+          'ipc_sync_message_filter.h',
         ],
         'include_dirs': [
           '..',
         ],
       }],
     ],
   },
   'targets': [
     {
       'target_name': 'ipc',
@@ skipping 41 matching lines @@
       ],
     }],
   ],
 }
 
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