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

cc/scheduler/delay_based_time_source.h

Index: cc/scheduler/delay_based_time_source.h
diff --git a/cc/scheduler/delay_based_time_source.h b/cc/scheduler/delay_based_time_source.h
index ea03f9d9742ed2297cba0008e589d10fc3107a68..da968a6f017dca57e6e3b20882123e5f13197395 100644
--- a/cc/scheduler/delay_based_time_source.h
+++ b/cc/scheduler/delay_based_time_source.h
@@ -12,11 +12,17 @@
 #include "cc/base/cc_export.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class TracedValue;
 }
-class SingleThreadTaskRunner;
+
+// 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 SingleThreadTaskRunner;
+}  // namespace base
 
 namespace cc {