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

cc/blink/web_layer_impl.h

Index: cc/blink/web_layer_impl.h
diff --git a/cc/blink/web_layer_impl.h b/cc/blink/web_layer_impl.h
index bced59805c27fadd62d73f0b97cde5627ce8428f..b33e92d995780dd3f071a171c02cdf709564beb2 100644
--- a/cc/blink/web_layer_impl.h
+++ b/cc/blink/web_layer_impl.h
@@ -31,9 +31,12 @@ struct WebFloatRect;
 }
 
 namespace base {
-namespace debug {
+namespace trace_event {
 class ConvertableToTraceFormat;
 }
+namespace debug {
+using ::base::trace_event::ConvertableToTraceFormat;
+}
 }
 
 namespace cc {