Add an intrinsified early out path for Dart timeline calls

runtime/lib/timeline.cc

Index: runtime/lib/timeline.cc
diff --git a/runtime/lib/timeline.cc b/runtime/lib/timeline.cc
index d8bef457202901fbf7c4ac1b5f7bc84760635924..b5b397db5ee0ae40cae014ee6ce6d81c547084ce 100644
--- a/runtime/lib/timeline.cc
+++ b/runtime/lib/timeline.cc
@@ -15,6 +15,17 @@ namespace dart {
 
 // Native implementations for the dart:developer library.
 
+DEFINE_NATIVE_ENTRY(Timeline_isDartStreamEnabled, 0) {
+  if (!FLAG_support_timeline) {
+    return Bool::False().raw();
+  }
+  if (Timeline::GetDartStream()->enabled()) {
+    return Bool::True().raw();
+  }
+  return Bool::False().raw();
+}
+
+
 DEFINE_NATIVE_ENTRY(Timeline_getIsolateNum, 0) {
   return Integer::New(static_cast<int64_t>(isolate->main_port()), Heap::kOld);
 }