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

cc/trees/layer_tree_impl.h

 // Copyright 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 CC_TREES_LAYER_TREE_IMPL_H_
 #define CC_TREES_LAYER_TREE_IMPL_H_
 
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/containers/hash_tables.h"
 #include "base/values.h"
 #include "cc/base/scoped_ptr_vector.h"
 #include "cc/base/swap_promise.h"
 #include "cc/base/synced_property.h"
 #include "cc/layers/layer_impl.h"
 #include "cc/output/renderer.h"
 #include "cc/resources/ui_resource_client.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 ContextProvider;
 class DebugRectHistory;
 class FrameRateCounter;
 class HeadsUpDisplayLayerImpl;
 class LayerScrollOffsetDelegateProxy;
 class LayerTreeDebugState;
 class LayerTreeHostImpl;
@@ skipping 380 matching lines @@
 
   scoped_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_IMPL_H_