Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/generics_double_substitution_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.generics_double_substitution;
 
+@MirrorsUsed(targets: "test.generics_double_substitution")
 import 'dart:mirrors';
 import 'package:expect/expect.dart';
 
 class A<R> {}
 class B<S> {}
 class C<T> extends B<A<T>> {
   A<T> field;
   A<T> returnType() {}
   parameterType(A<T> param) {}
 }
 
 main() {
   ClassMirror cOfString = reflect(new C<String>()).type;
   ClassMirror aOfString = reflect(new A<String>()).type;
 
   VariableMirror field = cOfString.declarations[#field];
   Expect.equals(aOfString, field.type);
 
   MethodMirror returnType = cOfString.declarations[#returnType];
   Expect.equals(aOfString, returnType.returnType);
 
   MethodMirror parameterType = cOfString.declarations[#parameterType];
   Expect.equals(aOfString, parameterType.parameters.single.type);
 
   ClassMirror typeArgOfSuperclass = cOfString.superclass.typeArguments.single;
   Expect.equals(aOfString, typeArgOfSuperclass);  /// 01: ok
 }