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 a7c846b7009e04c517f9eea6e05886f02a3db506..f1935152e7a583a33e8c8eaf883508397b2b3c7f 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