Dart VM: Simplify token positions in the translation of await.

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 c731c33df3d3368c7dbf191dbd112f1a213a8214..974259e158e15a22a031f00294b73fd1b48f0aae 100644
--- a/runtime/vm/ast_transformer.cc
+++ b/runtime/vm/ast_transformer.cc
@@ -215,9 +215,7 @@ void AwaitTransformer::VisitAwaitNode(AwaitNode* node) {
                      new (Z) LiteralNode(token_pos, Object::null_instance())),
       error_ne_null_branch, NULL));
 
-  LocalVariable* result = AddNewTempVarToPreamble(
-      new (Z) LoadLocalNode(token_pos, result_param), ST(node->token_pos()));
-  result_ = new (Z) LoadLocalNode(token_pos, result);
+  result_ = MakeName(new (Z) LoadLocalNode(token_pos, result_param));
 }