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

cc/trees/proxy.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_TREES_PROXY_H_
 #define CC_TREES_PROXY_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "cc/base/cc_export.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 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;
-}
+}  // namespace base
 
 namespace gfx {
 class Rect;
 class Vector2d;
 }
 
 namespace cc {
 class BlockingTaskRunner;
 class LayerTreeDebugState;
 class OutputSurface;
@@ skipping 122 matching lines @@
   explicit DebugScopedSetMainThreadBlocked(Proxy* proxy) {}
   ~DebugScopedSetMainThreadBlocked() {}
  private:
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetMainThreadBlocked);
 };
 #endif
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROXY_H_