content: Cleanup class/struct forward declarations

content/browser/renderer_host/render_widget_helper.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_RENDERER_HOST_RENDER_WIDGET_HELPER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HELPER_H_
 
 #include <stdint.h>
 
 #include <map>
 
 #include "base/atomic_sequence_num.h"
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/process/process.h"
 #include "content/common/render_message_filter.mojom.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/content_browser_client.h"
 #include "content/public/browser/global_request_id.h"
 #include "content/public/common/window_container_type.h"
 #include "third_party/WebKit/public/web/WebPopupType.h"
 #include "ui/gfx/native_widget_types.h"
 
-namespace IPC {
-class Message;
-}
-
 namespace content {
 class ResourceDispatcherHostImpl;
 class SessionStorageNamespace;
 
 // Instantiated per RenderProcessHost to provide various optimizations on
 // behalf of a RenderWidgetHost.  This class bridges between the IO thread
 // where the RenderProcessHost's MessageFilter lives and the UI thread where
 // the RenderWidgetHost lives.
 //
 //
@@ skipping 101 matching lines @@
   base::AtomicSequenceNumber next_routing_id_;
 
   ResourceDispatcherHostImpl* resource_dispatcher_host_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHelper);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HELPER_H_