Reland of Use a token to initialise ChannelMojo and MojoApplication everywhere.

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 73 matching lines @@
   CacheStorageMsgStart,
   ServiceWorkerMsgStart,
   MessagePortMsgStart,
   EmbeddedWorkerMsgStart,
   EmbeddedWorkerContextMsgStart,
   CastMsgStart,
   CdmMsgStart,
   ScreenOrientationMsgStart,
   MediaStreamTrackMetricsHostMsgStart,
   ChromeExtensionMsgStart,
-  MojoMsgStart,
   TranslateMsgStart,
   CldDataProviderMsgStart,
   PushMessagingMsgStart,
   GinJavaBridgeMsgStart,
   ChromeUtilityPrintingMsgStart,
   AecDumpMsgStart,
   OzoneGpuMsgStart,
   ChromeUtilityExtensionsMsgStart,
   PlatformNotificationMsgStart,
   PDFMsgStart,
@@ skipping 27 matching lines @@
   DistillerMsgStart,
   StartupMetricMsgStart,
   ArcCameraMsgStart,
   DWriteFontProxyMsgStart,
   MediaPlayerDelegateMsgStart,
   SurfaceViewManagerMsgStart,
   LastIPCMsgStart  // Must come last.
 };
 
 #endif  // IPC_IPC_MESSAGE_START_H_