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

cc/resources/pixel_buffer_tile_task_worker_pool.h

Index: cc/resources/pixel_buffer_tile_task_worker_pool.h
diff --git a/cc/resources/pixel_buffer_tile_task_worker_pool.h b/cc/resources/pixel_buffer_tile_task_worker_pool.h
index edff89a13b21ff0102dbcfddac7f33899709e8af..8ee4b9cae012f8c1f63df00eed036bb314b94be1 100644
--- a/cc/resources/pixel_buffer_tile_task_worker_pool.h
+++ b/cc/resources/pixel_buffer_tile_task_worker_pool.h
@@ -16,18 +16,11 @@
 #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 ResourceProvider;