Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/generics_dynamic_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 lib;
+
+@MirrorsUsed(targets: "lib")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class A<T> {}
 class B<T extends A> extends A implements C{
   A m(A a) {}
   A field;
 }
 class C<S,T> {}
 class D extends A<int> {}
@@ skipping 42 matching lines @@
   Expect.equals(dynamicMirror, returnTypeA.typeArguments.single);
   Expect.equals(dynamicMirror, parameterTypeA.typeArguments.single);
   Expect.equals(dynamicMirror, fieldTypeA.typeArguments.single);
   Expect.equals(dynamicMirror, upperBoundA.typeArguments.single);
   Expect.equals(dynamicMirror, cInstance.typeArguments.first);
   Expect.equals(dynamicMirror, cInstance.typeArguments.last);
   Expect.equals(dynamicMirror, cNestedInstance.typeArguments.last);
   Expect.equals(dynamicMirror, cTypeArgument.typeArguments.first);
   Expect.equals(dynamicMirror, cTypeArgument.typeArguments.last);  
 }