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

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index f52b5de77ce21807418f2b26e0d19c41b6f03449..a789ae280f8c8f90490db1bb8a49c285acdbc26d 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -40,14 +40,19 @@
 #include "ui/gfx/transform.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class ConvertableToTraceFormat;
 class TracedValue;
 }
 
-class DictionaryValue;
+namespace debug {
+using ::base::trace_event::ConvertableToTraceFormat;
+using ::base::trace_event::TracedValue;
 }
 
+class DictionaryValue;
+}  // namespace base
+
 namespace cc {
 
 class LayerTreeHostImpl;