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

cc/scheduler/scheduler_settings.h

Index: cc/scheduler/scheduler_settings.h
diff --git a/cc/scheduler/scheduler_settings.h b/cc/scheduler/scheduler_settings.h
index 4ff3c7eb5f7a3bcce279d38dd28d6b91e8dc4716..15d6a72edd1c17f0e56e179be7fb53426e821735 100644
--- a/cc/scheduler/scheduler_settings.h
+++ b/cc/scheduler/scheduler_settings.h
@@ -11,10 +11,17 @@
 #include "cc/base/cc_export.h"
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class ConvertableToTraceFormat;
 }
+
+// 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;
 }
+}  // namespace base
 
 namespace cc {
 class LayerTreeSettings;