content: Cleanup class/struct forward declarations

content/public/browser/devtools_external_agent_proxy.h

 // Copyright (c) 2013 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_PUBLIC_BROWSER_DEVTOOLS_EXTERNAL_AGENT_PROXY_H_
 #define CONTENT_PUBLIC_BROWSER_DEVTOOLS_EXTERNAL_AGENT_PROXY_H_
 
 #include <string>
 
 #include "content/common/content_export.h"
 
 namespace content {
 
-class DevToolsAgentHost;
-class DevToolsExternalAgentProxyDelegate;
-
 // Describes interface for communication with an external DevTools agent.
 class DevToolsExternalAgentProxy {
  public:
   // Sends the message to the client host.
   virtual void DispatchOnClientHost(const std::string& message) = 0;
 
   // Informs the client that the connection has closed.
   virtual void ConnectionClosed() = 0;
 
   virtual ~DevToolsExternalAgentProxy() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DEVTOOLS_EXTERNAL_AGENT_PROXY_H_