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

cc/output/filter_operation.h

Index: cc/output/filter_operation.h
diff --git a/cc/output/filter_operation.h b/cc/output/filter_operation.h
index 157db9983d32b830119589acafb940cc179293fe..fc14cb1017ade130fe2cfa6c1bf7e70a4b92e825 100644
--- a/cc/output/filter_operation.h
+++ b/cc/output/filter_operation.h
@@ -16,17 +16,11 @@
 #include "ui/gfx/geometry/point.h"
 
 namespace base {
-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;
+class Value;
 }
-class Value;
-}  // namespace base
 
 namespace cc {