Allow optional initializing formals again

tests/language/src/ParameterInitializer5NegativeTest.dart

Index: tests/language/src/ParameterInitializer5NegativeTest.dart
===================================================================
--- tests/language/src/ParameterInitializer5NegativeTest.dart	(revision 0)
+++ tests/language/src/ParameterInitializer5NegativeTest.dart	(revision 0)
@@ -0,0 +1,15 @@
+// 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.
+
+// Fails because this.x parameter is used in initializer expression.
+
+class Foo {
+  var x, y;
+  Foo(this.x): y = x { }
+}
+
+
+main() {
+  new Foo(12);
+}