content: Cleanup class/struct forward declarations

content/browser/tracing/tracing_controller_impl.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_BROWSER_TRACING_TRACING_CONTROLLER_IMPL_H_
 #define CONTENT_BROWSER_TRACING_TRACING_CONTROLLER_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <list>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/tracing_agent.h"
 #include "content/public/browser/tracing_controller.h"
 
 namespace base {
 class RefCountedString;
-class RefCountedMemory;
 }
 
 namespace content {
 
 class TraceMessageFilter;
 class TracingUI;
 
 // An implementation of this interface is passed when constructing a
 // TraceDataSink, and receives chunks of the final trace data as it's being
 // constructed.
@@ skipping 207 matching lines @@
   scoped_refptr<TraceDataSink> trace_data_sink_;
   scoped_refptr<TraceDataSink> monitoring_data_sink_;
   std::unique_ptr<base::DictionaryValue> metadata_;
 
   DISALLOW_COPY_AND_ASSIGN(TracingControllerImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_TRACING_TRACING_CONTROLLER_IMPL_H_