content: Cleanup class/struct forward declarations

content/common/child_process_host_impl.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 CONTENT_COMMON_CHILD_PROCESS_HOST_IMPL_H_
 #define CONTENT_COMMON_CHILD_PROCESS_HOST_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/shared_memory.h"
 #include "base/memory/singleton.h"
 #include "base/process/process.h"
 #include "base/strings/string16.h"
 #include "build/build_config.h"
 #include "content/public/common/child_process_host.h"
 #include "ipc/ipc_listener.h"
 
 namespace IPC {
 class MessageFilter;
 }
 
-namespace gpu {
-struct SyncToken;
-}
-
 namespace content {
 class ChildProcessHostDelegate;
 
 // Provides common functionality for hosting a child process and processing IPC
 // messages between the host and the child process. Users are responsible
 // for the actual launching and terminating of the child processes.
 class CONTENT_EXPORT ChildProcessHostImpl : public ChildProcessHost,
                                             public IPC::Listener {
  public:
   ~ChildProcessHostImpl() override;
@@ skipping 60 matching lines @@
   // thread, we don't have a IPC::ChannelProxy and so we manage filters
   // manually.
   std::vector<scoped_refptr<IPC::MessageFilter> > filters_;
 
   DISALLOW_COPY_AND_ASSIGN(ChildProcessHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_CHILD_PROCESS_HOST_IMPL_H_