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

cc/resources/one_copy_tile_task_worker_pool.h

Index: cc/resources/one_copy_tile_task_worker_pool.h
diff --git a/cc/resources/one_copy_tile_task_worker_pool.h b/cc/resources/one_copy_tile_task_worker_pool.h
index 85b3f32e3714ec05639ecb33e3dcd70233029c02..4568d354df4cd1ebeb4bedb2bb3b34339ef5b463 100644
--- a/cc/resources/one_copy_tile_task_worker_pool.h
+++ b/cc/resources/one_copy_tile_task_worker_pool.h
@@ -15,18 +15,11 @@
 #include "cc/resources/tile_task_worker_pool.h"
 
 namespace base {
-namespace trace_event {
+namespace debug {
 class ConvertableToTraceFormat;
 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::ConvertableToTraceFormat;
-using ::base::trace_event::TracedValue;
 }
-}  // namespace base
 
 namespace cc {
 class ResourcePool;