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

base/trace_event/trace_event_argument.h

Index: base/trace_event/trace_event_argument.h
diff --git a/base/trace_event/trace_event_argument.h b/base/trace_event/trace_event_argument.h
index 08a5b50057f81735af1edc2c06fa6880553e0d5b..43a0f38ddde518ab78f7508bc3969e6a315e778f 100644
--- a/base/trace_event/trace_event_argument.h
+++ b/base/trace_event/trace_event_argument.h
@@ -16,7 +16,7 @@ class DictionaryValue;
 class ListValue;
 class Value;
 
-namespace debug {
+namespace trace_event {
 
 class BASE_EXPORT TracedValue : public ConvertableToTraceFormat {
  public:
@@ -53,6 +53,14 @@ class BASE_EXPORT TracedValue : public ConvertableToTraceFormat {
   DISALLOW_COPY_AND_ASSIGN(TracedValue);
 };
 
+}  // namespace trace_event
+}  // namespace base
+
+// 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 base {
+namespace debug {
+using base::trace_event::TracedValue;
 }  // namespace debug
 }  // namespace base