Replace image_messages.h with Mojo service

ipc/ipc_message_start.h

 // Copyright 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.
 
 #ifndef IPC_IPC_MESSAGE_START_H_
 #define IPC_IPC_MESSAGE_START_H_
 
 // Used by IPC_BEGIN_MESSAGES so that each message class starts from a unique
 // base.  Messages have unique IDs across channels in order for the IPC logging
 // code to figure out the message class from its ID.
@@ skipping 35 matching lines @@
   DeviceOrientationMsgStart,
   AudioMsgStart,
   MidiMsgStart,
   ChromeMsgStart,
   DragMsgStart,
   PrintMsgStart,
   SpellCheckMsgStart,
   ExtensionMsgStart,
   VideoCaptureMsgStart,
   QuotaMsgStart,
-  ImageMsgStart,

[Anand Mistry (off Chromium), 2015/06/16 07:51:36]

On second thought (and after looking over some other code), add this back.
Instead, add a comment that this has been removed. My concern is that by
removing this, the message types change and could break something (I suspect app
shim will break).

[leonhsl(Using Gerrit), 2015/06/23 02:18:02]

Done.

   TextInputClientMsgStart,
   ChromeUtilityMsgStart,
   MediaStreamMsgStart,
   ChromeBenchmarkingMsgStart,
   JavaBridgeMsgStart,
   GamepadMsgStart,
   ShellMsgStart,
   AccessibilityMsgStart,
   PrefetchMsgStart,
   PrerenderMsgStart,
@@ skipping 55 matching lines @@
   CastCryptoMsgStart,
   CastChannelMsgStart,
   DataReductionProxyStart,
   ContentSettingsMsgStart,
   ChromeAppBannerMsgStart,
   SafeJsonParserMsgStart,
   LastIPCMsgStart  // Must come last.
 };
 
 #endif  // IPC_IPC_MESSAGE_START_H_