Add an intrinsified early out path for Dart timeline calls

runtime/lib/timeline.cc

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "include/dart_api.h"
 
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/os.h"
 #include "vm/timeline.h"
 
 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);
 }
 
 
 DEFINE_NATIVE_ENTRY(Timeline_getNextAsyncId, 0) {
   if (!FLAG_support_timeline) {
     return Integer::New(0);
   }
   TimelineEventRecorder* recorder = Timeline::recorder();
@@ skipping 187 matching lines @@
       args.ToCString());
 
   event->Instant("", start.AsInt64Value());
   // json was allocated in the zone and a copy will be stored in event.
   event->CompleteWithPreSerializedJSON(json);
 
   return Object::null();
 }
 
 }  // namespace dart