extensions: Cleanup class/struct fwd declarations

extensions/renderer/dom_activity_logger.h

 // Copyright 2014 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 EXTENSIONS_RENDERER_DOM_ACTIVITY_LOGGER_H_
 #define EXTENSIONS_RENDERER_DOM_ACTIVITY_LOGGER_H_
 
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "extensions/common/dom_action_types.h"
 #include "third_party/WebKit/public/web/WebDOMActivityLogger.h"
 #include "v8/include/v8.h"
 
 namespace base {
 class ListValue;
 }
 
 namespace blink {
 class WebString;
 class WebURL;
 }
 
-namespace content {
-class V8ValueConverter;
-}
-
 namespace extensions {
 
 // Used to log DOM API calls from within WebKit. The events are sent via IPC to
 // extensions::ActivityLog for recording and display.
 class DOMActivityLogger: public blink::WebDOMActivityLogger {
  public:
   static const int kMainWorldId = 0;
   explicit DOMActivityLogger(const std::string& extension_id);
   ~DOMActivityLogger() override;
 
@@ skipping 43 matching lines @@
   // The id of the extension with which this logger is associated.
   std::string extension_id_;
 
   DISALLOW_COPY_AND_ASSIGN(DOMActivityLogger);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_DOM_ACTIVITY_LOGGER_H_