base: Cleanup class/struct forward declarations

base/trace_event/trace_event_impl.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 BASE_TRACE_EVENT_TRACE_EVENT_IMPL_H_
 #define BASE_TRACE_EVENT_TRACE_EVENT_IMPL_H_
 
 #include <stdint.h>
 
@@ skipping 10 matching lines @@
 #include "base/observer_list.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_local.h"
 #include "base/trace_event/trace_event_memory_overhead.h"
 #include "build/build_config.h"
 
 namespace base {
-
-class WaitableEvent;
-class MessageLoop;
-
 namespace trace_event {
 
 typedef base::Callback<bool(const char* arg_name)> ArgumentNameFilterPredicate;
 
 typedef base::Callback<bool(const char* category_group_name,
                             const char* event_name,
                             ArgumentNameFilterPredicate*)>
     ArgumentFilterPredicate;
 
 // For any argument of type TRACE_VALUE_TYPE_CONVERTABLE the provided
@@ skipping 134 matching lines @@
   unsigned char arg_types_[kTraceMaxNumArgs];
   char phase_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceEvent);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_IMPL_H_