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

cc/output/filter_operations.h

Index: cc/output/filter_operations.h
diff --git a/cc/output/filter_operations.h b/cc/output/filter_operations.h
index 8e3793321cfc6dd043c827df8dc2a9feefa80f5f..a8c206eacd1b0593cfc3f4400420d9f3ae63c4e0 100644
--- a/cc/output/filter_operations.h
+++ b/cc/output/filter_operations.h
@@ -12,17 +12,11 @@
 #include "cc/output/filter_operation.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 {