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

runtime/vm/ast_transformer.cc

Index: runtime/vm/ast_transformer.cc
diff --git a/runtime/vm/ast_transformer.cc b/runtime/vm/ast_transformer.cc
index af1331c59d3a5299ddc9fbb6779d5b4d1dae300a..7886349a22dc8d7f99ee5d72d4c36de81abe6445 100644
--- a/runtime/vm/ast_transformer.cc
+++ b/runtime/vm/ast_transformer.cc
@@ -136,7 +136,10 @@ void AwaitTransformer::VisitAwaitNode(AwaitNode* node) {
   //   :await_temp_var_X = <expr>;
   //   AwaitMarker(kNewContinuationState);
   //   :result_param = _awaitHelper(
-  //      :await_temp_var_X, :async_then_callback, :async_catch_error_callback);
+  //      :await_temp_var_X,
+  //      :async_then_callback,
+  //      :async_catch_error_callback,
+  //      :async_op);
   //   return;  // (return_type() == kContinuationTarget)
   //
   //   :saved_try_ctx_var = :await_saved_try_ctx_var_y;
@@ -165,7 +168,10 @@ void AwaitTransformer::VisitAwaitNode(AwaitNode* node) {
   preamble_->Add(await_marker);
 
   // :result_param = _awaitHelper(
-  //      :await_temp, :async_then_callback, :async_catch_error_callback)
+  //      :await_temp,
+  //      :async_then_callback,
+  //      :async_catch_error_callback,
+  //      :async_op)
   const Library& async_lib = Library::Handle(Library::AsyncLibrary());
   const Function& async_await_helper = Function::ZoneHandle(
       Z, async_lib.LookupFunctionAllowPrivate(Symbols::AsyncAwaitHelper()));
@@ -177,6 +183,7 @@ void AwaitTransformer::VisitAwaitNode(AwaitNode* node) {
       new (Z) LoadLocalNode(token_pos, async_then_callback));
   async_await_helper_args->Add(
       new (Z) LoadLocalNode(token_pos, async_catch_error_callback));
+  async_await_helper_args->Add(new (Z) LoadLocalNode(token_pos, async_op));
   StaticCallNode* await_helper_call = new (Z) StaticCallNode(
       node->token_pos(), async_await_helper, async_await_helper_args);