Move IPCMessageStart enum into it own directory with security team OWNERS, so that new message file…

ipc/ipc.gypi

 # 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.
 
 {
   'target_defaults': {
     'variables': {
       'ipc_target': 0,
     },
     'target_conditions': [
@@ skipping 18 matching lines @@
           'ipc_descriptors.h',
           'ipc_export.h',
           'ipc_forwarding_message_filter.cc',
           'ipc_forwarding_message_filter.h',
           'ipc_listener.h',
           'ipc_logging.cc',
           'ipc_logging.h',
           'ipc_message.cc',
           'ipc_message.h',
           'ipc_message_macros.h',
+          'ipc_message_start.h',
           'ipc_message_utils.cc',
           'ipc_message_utils.h',
           'ipc_param_traits.h',
           'ipc_platform_file.cc',
           'ipc_platform_file.h',
           'ipc_sender.h',
           'ipc_switches.cc',
           'ipc_switches.h',
           'ipc_sync_channel.cc',
           'ipc_sync_channel.h',
@@ skipping 19 matching lines @@
             'sources!': [
               'ipc_channel.cc',
               'ipc_channel_posix.cc',
             ],
           }],
         ],
       }],
     ],
   },
 }