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..acd34384374bb9252e3fd8fa928dcc061fcb846d 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -40,13 +40,20 @@
 #include "ui/gfx/transform.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class ConvertableToTraceFormat;
 class TracedValue;
 }
 
-class DictionaryValue;
+// 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::ConvertableToTraceFormat;
+using ::base::trace_event::TracedValue;
 }
+class DictionaryValue;
+}  // namespace base
 
 namespace cc {