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

content/renderer/scheduler/task_queue_selector.h

Index: content/renderer/scheduler/task_queue_selector.h
diff --git a/content/renderer/scheduler/task_queue_selector.h b/content/renderer/scheduler/task_queue_selector.h
index fe20847ad63669639c6dc4dae7892bf6eba4abf9..efe9bcf91819e731a2e1fbe3f5a794d7746a8808 100644
--- a/content/renderer/scheduler/task_queue_selector.h
+++ b/content/renderer/scheduler/task_queue_selector.h
@@ -11,8 +11,14 @@
 
 namespace base {
 class TaskQueue;
-namespace debug {
+namespace trace_event {
 class TracedValue;
+}  // namespace trace_event
+
+// 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;
 }  // namespace debug
 }  // namespace base