Track the 'awaiter return' call stack use it to detect uncaught exceptions in async functions

runtime/vm/object_service.cc

Index: runtime/vm/object_service.cc
diff --git a/runtime/vm/object_service.cc b/runtime/vm/object_service.cc
index 5591052ae7fa3223f6af1c6f9293fae4ff856c78..adab7faca6cf67b67a961fa1cbba1c56343af87b 100644
--- a/runtime/vm/object_service.cc
+++ b/runtime/vm/object_service.cc
@@ -869,6 +869,11 @@ void Code::PrintJSONImpl(JSONStream* stream, bool ref) const {
 }
 
 
+void Code::SetAwaitTokenPositions(const Array& await_token_positions) const {
+  StorePointer(&raw_ptr()->await_token_positions_, await_token_positions.raw());
+}
+
+
 void Context::PrintJSONImpl(JSONStream* stream, bool ref) const {
   JSONObject jsobj(stream);
   // TODO(turnidge): Should the user level type for Context be Context