Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/constructors_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.constructors_test;
 
+@MirrorsUsed(targets: "test.constructors_test")
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 import 'stringify.dart';
 
 constructorsOf(ClassMirror cm) {
   var result = new Map();
   cm.declarations.forEach((k,v) {
     if(v is MethodMirror && v.isConstructor) result[k] = v;
@@ skipping 46 matching lines @@
   expect('[s()]',
          fooConstructors.values.map((m) => m.constructorName).toList());
   expect('[s()]',
          barConstructors.values.map((m) => m.constructorName).toList());
   expect('[s(named)]',
          bazConstructors.values.map((m) => m.constructorName).toList());
   expect('[s(), s(named)]',
          bizConstructors.values.map((m) => m.constructorName).toList()
              ..sort(compareSymbols));
 }