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

cc/blink/web_layer_impl.h

Index: cc/blink/web_layer_impl.h
diff --git a/cc/blink/web_layer_impl.h b/cc/blink/web_layer_impl.h
index b0d472ae1535d68342bdba30c864f4559eb2ddb1..111c6cf703ea5000cc9c36085b6b705ca6db809e 100644
--- a/cc/blink/web_layer_impl.h
+++ b/cc/blink/web_layer_impl.h
@@ -31,16 +31,10 @@
 }
 
 namespace base {
-namespace trace_event {
+namespace debug {
 class ConvertableToTraceFormat;
 }
-
-// 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::ConvertableToTraceFormat;
 }
-}  // namespace base
 
 namespace cc {
 class Layer;