content: Cleanup class/struct forward declarations

content/browser/devtools/devtools_agent_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_BROWSER_DEVTOOLS_DEVTOOLS_AGENT_HOST_IMPL_H_
 #define CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_AGENT_HOST_IMPL_H_
 
 #include <stdint.h>
 
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "content/browser/devtools/devtools_io_context.h"
 #include "content/browser/devtools/protocol/devtools_protocol_delegate.h"
 #include "content/common/content_export.h"
 #include "content/common/devtools_messages.h"
 #include "content/public/browser/devtools_agent_host.h"
 
-namespace IPC {
-class Message;
-}
-
 namespace content {
 
 class BrowserContext;
 class DevToolsSession;
 
 // Describes interface for managing devtools agents from the browser process.
 class CONTENT_EXPORT DevToolsAgentHostImpl : public DevToolsAgentHost,
                                              public DevToolsProtocolDelegate {
  public:
   // Informs the hosted agent that a client host has attached.
@@ skipping 77 matching lines @@
   SendMessageCallback callback_;
   std::string message_buffer_;
   uint32_t message_buffer_size_;
   std::string state_cookie_;
   int last_call_id_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVTOOLS_DEVTOOLS_AGENT_HOST_IMPL_H_