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

cc/base/math_util.h

Index: cc/base/math_util.h
diff --git a/cc/base/math_util.h b/cc/base/math_util.h
index 72f03992d62857e2245ad2921bfc39915740b7e7..d9cc43b552eb1042381569f0ff377a1d3de865d0 100644
--- a/cc/base/math_util.h
+++ b/cc/base/math_util.h
@@ -21,17 +21,10 @@
 
 namespace base {
 class Value;
-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 gfx {
 class QuadF;