Add a trace-event for each runtime-stats timer

src/tracing/trace-event.cc

Index: src/tracing/trace-event.cc
diff --git a/src/tracing/trace-event.cc b/src/tracing/trace-event.cc
index 04f1f2e2ea0d0a8df9f504b24954cfc7857cd413..a2c2b830842854316ee81661396bc36c6c91733d 100644
--- a/src/tracing/trace-event.cc
+++ b/src/tracing/trace-event.cc
@@ -10,6 +10,10 @@ namespace v8 {
 namespace internal {
 namespace tracing {
 
+// A global flag used as a shortcut to check for the
+// v8.runtime category due to its high frequency use.
+int kRuntimeCallsTracingEnabled = 0;
+
 v8::Platform* TraceEventHelper::GetCurrentPlatform() {
   return v8::internal::V8::GetCurrentPlatform();
 }