Fix product build

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 498130474c0a56c38a2a90e755c8bd4ba7d5bf5d..8f3cb9764c5cb10600f17e19c39e48d7ff920198 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5962,6 +5962,9 @@ DART_EXPORT void Dart_SetEmbedderTimelineCallbacks(
     Dart_EmbedderTimelineStartRecording start_recording,
     Dart_EmbedderTimelineStopRecording stop_recording,
     Dart_EmbedderTimelineGetTimeline get_timeline) {
+  if (!FLAG_support_timeline) {
+    return;
+  }
   Timeline::set_start_recording_cb(start_recording);
   Timeline::set_stop_recording_cb(stop_recording);
   Timeline::set_get_timeline_cb(get_timeline);