Add @MirrorsUsed annotations to speed up tests.

tests/lib/mirrors/delegate_call_through_getter_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.invoke_call_through_getter;
 
+@MirrorsUsed(targets: "test.invoke_call_through_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 19 matching lines @@
 
   Expect.equals('1 5 6', f.fakeFunctionCall(5, 6));
   Expect.equals('7, 8', f.fakeFunctionNSM(7, 8));
   Expect.equals('2 C 9 10', f.closure(9, 10));
   Expect.equals('3 C 11 12 13 null', f.closureOpt(11, 12, 13));
   Expect.equals('4 C 14 15 null 16', f.closureNamed(14, 15, w: 16));
   Expect.equals('DNU', f.doesNotExist(17, 18));
   Expect.throws(() => f.closure('wrong arity'), (e) => e is NoSuchMethodError);
   Expect.throws(() => f.notAClosure(), (e) => e is NoSuchMethodError);
 }