Implement VariableMirror.isConst in the VM and ParameterMirror.isConst in dart2js.

tests/lib/mirrors/parameter_is_const_test.dart

 // Copyright (c) 2013, 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.
 
+library test.parameter_is_const;
+
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
-class Foo {
+class Class {
+  foo(
+  const /// 01: compile-time error
+  param) {}
 }
 
 main() {
-  Expect.stringEquals('Foo', '${new Foo().runtimeType}');
-  Expect.stringEquals('foo', MirrorSystem.getName(new Symbol('foo')));
+  MethodMirror mm = reflectClass(Class).declarations[#foo];
+  Expect.isFalse(mm.parameters.single.isConst);
 }