chrome: Cleanup class/struct forward declarations

chrome/test/chromedriver/chrome/frame_tracker.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 CHROME_TEST_CHROMEDRIVER_CHROME_FRAME_TRACKER_H_
 #define CHROME_TEST_CHROMEDRIVER_CHROME_FRAME_TRACKER_H_
 
 #include <map>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "chrome/test/chromedriver/chrome/devtools_event_listener.h"
 
 namespace base {
 class DictionaryValue;
-class Value;
 }
 
 class DevToolsClient;
 class Status;
 
 // Tracks execution context creation.
 class FrameTracker : public DevToolsEventListener {
  public:
   explicit FrameTracker(DevToolsClient* client);
   ~FrameTracker() override;
 
   Status GetContextIdForFrame(const std::string& frame_id, int* context_id);
 
   // Overridden from DevToolsEventListener:
   Status OnConnected(DevToolsClient* client) override;
   Status OnEvent(DevToolsClient* client,
                  const std::string& method,
                  const base::DictionaryValue& params) override;
 
  private:
   std::map<std::string, int> frame_to_context_map_;
 
   DISALLOW_COPY_AND_ASSIGN(FrameTracker);
 };
 
 #endif  // CHROME_TEST_CHROMEDRIVER_CHROME_FRAME_TRACKER_H_