Fix parsing of named parameters (issue 243).

tests/language/src/NamedParameters9NegativeTest.dart

+// Copyright (c) 2011, 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.
+// Dart test program for testing named parameters.
+
+
+class NamedParameters9NegativeTest {
+
+  static int f(a [b = 42]) => b;  // Missing comma.
+
+  static testMain() {
+    try {
+      f(10, 25);
+    } catch (var e) {
+      // This is a negative test that should not compile.
+      // If it runs due to a bug, catch and ignore exceptions.
+    }
+  }
+}
+
+main() {
+  NamedParameters9NegativeTest.testMain();
+}