Fix LibraryMirror.invoke to call through the contents of an implicit getter.

tests/lib/mirrors/invoke_call_through_getter_previously_accessed_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;
 
 import 'dart:mirrors';
 
 import 'package:expect/expect.dart';
 
@@ skipping 112 matching lines @@
                 lm.invoke(#closure, [9, 10]).reflectee);
   Expect.equals('3 11 12 13 null',
                 lm.invoke(#closureOpt, [11, 12, 13]).reflectee);
   Expect.equals('4 14 15 null 16',
                 lm.invoke(#closureNamed, [14, 15], {#w: 16}).reflectee);
   Expect.throws(() => lm.invoke(#closure, ['wrong arity']),
                 (e) => e is NoSuchMethodError);
 }
 
 main() {
+  // Access the getters/closures at the base level in this variant.
   testInstanceBase();
   testInstanceReflective();
   testClassBase();
   testClassReflective();
   testLibraryBase();
   testLibraryReflective();
 }