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

cc/debug/traced_value.h

 // Copyright 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 CC_DEBUG_TRACED_VALUE_H_
 #define CC_DEBUG_TRACED_VALUE_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;
 }
-}  // namespace base
 
 namespace cc {
 
 class TracedValue {
  public:
   static void AppendIDRef(const void* id, base::debug::TracedValue* array);
   static void SetIDRef(const void* id,
                        base::debug::TracedValue* dict,
                        const char* name);
   static void MakeDictIntoImplicitSnapshot(base::debug::TracedValue* dict,
                                            const char* object_name,
                                            const void* id);
   static void MakeDictIntoImplicitSnapshotWithCategory(
       const char* category,
       base::debug::TracedValue* dict,
       const char* object_name,
       const void* id);
   static void MakeDictIntoImplicitSnapshotWithCategory(
       const char* category,
       base::debug::TracedValue* dict,
       const char* object_base_type_name,
       const char* object_name,
       const void* id);
 };
 
 }  // namespace cc
 
 #endif  // CC_DEBUG_TRACED_VALUE_H_