Revert of Move tracing namespace from base::debug to base::trace_event.

cc/scheduler/delay_based_time_source.h

 // Copyright 2011 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 CC_SCHEDULER_DELAY_BASED_TIME_SOURCE_H_
 #define CC_SCHEDULER_DELAY_BASED_TIME_SOURCE_H_
 
 #include <string>
 
 #include "base/memory/weak_ptr.h"
 #include "base/values.h"
 #include "cc/base/cc_export.h"
 
 namespace base {
-namespace trace_event {
+namespace debug {
 class TracedValue;
 }
-
-// TODO(ssid): remove these aliases after the tracing clients are moved to the
-// new trace_event namespace. See crbug.com/451032. ETA: March 2015
-namespace debug {
-using ::base::trace_event::TracedValue;
+class SingleThreadTaskRunner;
 }
-class SingleThreadTaskRunner;
-}  // namespace base
 
 namespace cc {
 
 class CC_EXPORT TimeSourceClient {
  public:
   virtual void OnTimerTick() = 0;
 
  protected:
   virtual ~TimeSourceClient() {}
 };
@@ skipping 82 matching lines @@
 
   std::string TypeString() const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DelayBasedTimeSourceHighRes);
 };
 
 }  // namespace cc
 
 #endif  // CC_SCHEDULER_DELAY_BASED_TIME_SOURCE_H_