Improve the mirror support for deferred loading.

tests/lib/mirrors/deferred_mirrors_metadata_test.dart

+// Copyright (c) 2014, 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.
+
 @A(const B())
 library main;
 
 @B()
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
 
 import "dart:math";
 
 import 'deferred_mirrors_metadata_lib.dart' deferred as lib1;
 
 class A {
   final B b;
   const A(this.b);
   String toString() => "A";
 }
 
 class B {
   const B();
   String toString() => "B";
 }
 
 class C {
   const C();
   String toString() => "C";
 }
 
+class D {
+  const D();
+  String toString() => "D";
+}
+
 void main() {
   asyncStart();
   lib1.loadLibrary().then((_) {
-    Expect.equals("ABC", lib1.foo());
+    Expect.equals("ABCD", lib1.foo());
+    new C();
+    new D();
     asyncEnd();
   });
 }