Move the common child process messages into their own file.

ipc/ipc_message_utils.h

 // Copyright (c) 2010 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.
 
 #ifndef IPC_IPC_MESSAGE_UTILS_H_
 #define IPC_IPC_MESSAGE_UTILS_H_
 #pragma once
 
 #include <algorithm>
 #include <string>
@@ skipping 55 matching lines @@
   IndexedDBMsgStart,
   PepperFileMsgStart,
   SpeechInputMsgStart,
   PepperMsgStart,
   AutoFillMsgStart,
   SafeBrowsingMsgStart,
   P2PMsgStart,
   SocketStreamMsgStart,
   ResourceMsgStart,
   FileSystemMsgStart,
+  ChildProcessMsgStart,
 };
 
 class DictionaryValue;
 class FilePath;
 class ListValue;
 class NullableString16;
 
 namespace base {
 class Time;
 class TimeDelta;
@@ skipping 1113 matching lines @@
     ReplyParam p(a, b, c, d, e);
     WriteParam(reply, p);
   }
 };
 
 //-----------------------------------------------------------------------------
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_MESSAGE_UTILS_H_