Cleanup remaining class/struct fwd declarations

ipc/ipc_channel_proxy.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.
 
 #ifndef IPC_IPC_CHANNEL_PROXY_H_
 #define IPC_IPC_CHANNEL_PROXY_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 16 matching lines @@
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace IPC {
 
 class ChannelFactory;
 class MessageFilter;
 class MessageFilterRouter;
-class SendCallbackHelper;
 
 //-----------------------------------------------------------------------------
 // IPC::ChannelProxy
 //
 // This class is a helper class that is useful when you wish to run an IPC
 // channel on a background thread.  It provides you with the option of either
 // handling IPC messages on that background thread or having them dispatched to
 // your main thread (the thread on which the IPC::ChannelProxy is created).
 //
 // The API for an IPC::ChannelProxy is very similar to that of an IPC::Channel.
@@ skipping 375 matching lines @@
   bool did_init_;
 
 #if defined(ENABLE_IPC_FUZZER)
   OutgoingMessageFilter* outgoing_message_filter_;
 #endif
 };
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_PROXY_H_