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

cc/base/math_util.h

Index: cc/base/math_util.h
diff --git a/cc/base/math_util.h b/cc/base/math_util.h
index d9cc43b552eb1042381569f0ff377a1d3de865d0..03062fca18152db740f93e20647a7665a6ddbd83 100644
--- a/cc/base/math_util.h
+++ b/cc/base/math_util.h
@@ -21,10 +21,18 @@
 
 namespace base {
 class Value;
-namespace debug {
+namespace trace_event {
 class TracedValue;
 }
+
+// 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::TracedValue;
 }
+}  // namespace base
+
 
 namespace gfx {
 class QuadF;