content: Cleanup class/struct forward declarations

content/browser/devtools/protocol/tracing_handler.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 CONTENT_BROWSER_DEVTOOLS_PROTOCOL_TRACING_HANDLER_H_
 #define CONTENT_BROWSER_DEVTOOLS_PROTOCOL_TRACING_HANDLER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <set>
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/trace_event/trace_event.h"
 #include "content/browser/devtools/protocol/devtools_protocol_dispatcher.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/tracing_controller.h"
 
 namespace base {
-class RefCountedString;
 class Timer;
 }
 
 namespace content {
 namespace devtools {
 
 class DevToolsIOContext;
 
 namespace tracing {
 
@@ skipping 59 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(TracingHandlerTest,
                            GetTraceConfigFromDevToolsConfig);
   DISALLOW_COPY_AND_ASSIGN(TracingHandler);
 };
 
 }  // namespace tracing
 }  // namespace devtools
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DEVTOOLS_PROTOCOL_TRACING_HANDLER_H_