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

ipc/ipc_message_macros.h

 // 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.
 
 // Defining IPC Messages
 //
 // Your IPC messages will be defined by macros inside of an XXX_messages.h
 // header file.  Most of the time, the system can automatically generate all
 // of messaging mechanism from these definitions, but sometimes some manual
 // coding is required.  In these cases, you will also have an XXX_messages.cc
 // implemation file as well.
 //
 // The senders of your messages will include your XXX_messages.h file to
 // get the full set of definitions they need to send your messages.
 //
 // Each XXX_messages.h file must be registered with the IPC system.  This
 // requires adding two things:
-//   - An XXXMsgStart value to the IPCMessageStart enum in ipc_message_utils.h
+//   - An XXXMsgStart value to the IPCMessageStart enum in ipc_message_start.h
 //   - An inclusion of XXX_messages.h file in a message generator .h file
 //
 // The XXXMsgStart value is an enumeration that ensures uniqueness for
 // each different message file.  Later, you will use this inside your
 // XXX_messages.h file before invoking message declaration macros:
 //     #define IPC_MESSAGE_START XXXMsgStart
 //       ( ... your macro invocations go here ... )
 //
 // Message Generator Files
 //
@@ skipping 975 matching lines @@
 // This corresponds to an enum value from IPCMessageStart.
 #define IPC_MESSAGE_CLASS(message) \
   IPC_MESSAGE_ID_CLASS(message.type())
 
 #endif  // IPC_IPC_MESSAGE_MACROS_H_
 
 // Clean up IPC_MESSAGE_START in this unguarded section so that the
 // XXX_messages.h files need not do so themselves.  This makes the
 // XXX_messages.h files easier to write.
 #undef IPC_MESSAGE_START