Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/inference_and_no_such_method_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.
 
 // Regression test for dart2js that did type inferencing on parameters
 // whose type may change at runtime due to an invocation through
 // [InstanceMirror.delegate].
 
+library lib;
+
+@MirrorsUsed(targets: "lib")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class A {
   noSuchMethod(im) {
     reflect(new B()).delegate(im);
   }
 }
 
 class B {
   foo(a) => a + 42;
 }
 
 main() {
   Expect.equals(42, new B().foo(0));
   Expect.throws(() => new A().foo('foo'),
                 (e) => e is ArgumentError || e is TypeError);
 }