Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/invoke_call_through_implicit_getter_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.
 
 library test.invoke_call_through_implicit_getter;
 
+@MirrorsUsed(targets: "test.invoke_call_through_implicit_getter")
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
 class FakeFunctionCall {
   call(x, y) => '1 $x $y';
 }
 class FakeFunctionNSM {
   noSuchMethod(msg) => msg.positionalArguments.join(', ');
 }
@@ skipping 120 matching lines @@
 
 main() {
   // Do not access the getters/closures at the base level in this variant.
   //testInstanceBase();
   testInstanceReflective();
   //testClassBase();
   testClassReflective();
   //testLibraryBase();
   testLibraryReflective();
 }