Avoid parsing formal type parameters a second time from inside an async body,

tests/language/regress_27659_test.dart

Index: tests/language/regress_27659_test.dart
diff --git a/tests/language/regress_27659_test.dart b/tests/language/regress_27659_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e40a88669916a429db6389a14a438b3f28604120
--- /dev/null
+++ b/tests/language/regress_27659_test.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+const String lineLength = '120';
+
+foo({lineLength: lineLength}) {
+  print(lineLength);
+}
+
+bar({lineLength: lineLength}) async {
+  print(lineLength);
+}
+
+baz([lineLength = lineLength]) {
+  print(lineLength);
+}
+
+qux([lineLength = lineLength]) async {
+  print(lineLength);
+}
+
+main() {
+  foo();
+  bar();
+  baz();
+  qux();
+}