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

cc/debug/traced_value.h

Index: cc/debug/traced_value.h
diff --git a/cc/debug/traced_value.h b/cc/debug/traced_value.h
index c5ea30aeddac261c84870913529da689d44bf750..402522f4e00f1dbf17ab69febd9be77c3b302f40 100644
--- a/cc/debug/traced_value.h
+++ b/cc/debug/traced_value.h
@@ -6,10 +6,17 @@
 #define CC_DEBUG_TRACED_VALUE_H_
 
 namespace base {
-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 cc {