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

cc/quads/shared_quad_state.h

Index: cc/quads/shared_quad_state.h
diff --git a/cc/quads/shared_quad_state.h b/cc/quads/shared_quad_state.h
index 0db23e195200b309c7752c87f9d456e7a4612b2e..ebf7d11986e01a30661fd73ac7a15bddbb312058 100644
--- a/cc/quads/shared_quad_state.h
+++ b/cc/quads/shared_quad_state.h
@@ -12,17 +12,11 @@
 #include "ui/gfx/transform.h"
 
 namespace base {
-namespace trace_event {
+namespace debug {
 class TracedValue;
 }
 class Value;
-
-// 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 {