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

cc/base/region.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 CC_BASE_REGION_H_
 #define CC_BASE_REGION_H_
 
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/skia_util.h"
 
 namespace base {
 class Value;
-namespace debug {
+namespace trace_event {
 class TracedValue;
 }
+
+// This is added temporarily. Once the renaming of namespace usages
+// accross all folders are done, this will be removed.
+// TODO(ssid): crrev.com/837303004
+namespace debug {
+using ::base::trace_event::TracedValue;
 }
+}  // namespace base
 
 namespace cc {
 class SimpleEnclosedRegion;
 
 class CC_EXPORT Region {
  public:
   Region();
   Region(const Region& region);
   Region(const gfx::Rect& rect);  // NOLINT(runtime/explicit)
   ~Region();
@@ skipping 99 matching lines @@
 
 inline Region UnionRegions(const Region& a, const gfx::Rect& b) {
   Region result = a;
   result.Union(b);
   return result;
 }
 
 }  // namespace cc
 
 #endif  // CC_BASE_REGION_H_