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

cc/resources/zero_copy_tile_task_worker_pool.h

Index: cc/resources/zero_copy_tile_task_worker_pool.h
diff --git a/cc/resources/zero_copy_tile_task_worker_pool.h b/cc/resources/zero_copy_tile_task_worker_pool.h
index 8d3c0cfbd10120d69faca2523ac9142fc9c02908..5f0ba9043cf4042c8f9461f7858c4501166a6eb6 100644
--- a/cc/resources/zero_copy_tile_task_worker_pool.h
+++ b/cc/resources/zero_copy_tile_task_worker_pool.h
@@ -11,10 +11,17 @@
 #include "cc/resources/tile_task_worker_pool.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class ConvertableToTraceFormat;
 }
+
+// This is added temporarily. Once the renaming of namespace usages
+// accross all folders are done, this will be removed.
+// TODO(ssid): crrev.com/837303004
+namespace debug {
+using ::base::trace_event::ConvertableToTraceFormat;
 }
+}  // namespace base
 
 namespace cc {
 class ResourceProvider;