Fix named arguments in await expressions

tests/language/await_regression_test.dart

Index: tests/language/await_regression_test.dart
===================================================================
--- tests/language/await_regression_test.dart	(revision 41962)
+++ tests/language/await_regression_test.dart	(working copy)
@@ -4,8 +4,8 @@
 //
 // VMOptions=--enable_async
 //
-// Regression test for issue 21536.
 
+
 import 'dart:async';
 import 'package:expect/expect.dart';
 
@@ -13,10 +13,26 @@
 
 manana(tequila) async => tequila;
 
-main() async {
+// Regression test for issue 21536.
+testNestedFunctions() async {
   var a = await later('Asterix').then((tonic) {
     return later(tonic);
   });
   var o = await manana('Obelix').then(manana);
   Expect.equals("$a and $o", "Asterix and Obelix");
 }
+
+addLater({a, b}) => new Future.value(a + b);
+
+// Regression test for issue 21480.
+testNamedArguments() async {
+  var sum = await addLater(a:5, b:10);
+  Expect.equals(sum, 15);
+  sum = await addLater(b:11, a:-11);
+  Expect.equals(sum, 0);
+}
+
+main() async {
+  testNestedFunctions();
+  testNamedArguments();
+}