Add code for new invalidation local ack system

sync/sync_notifier.gypi

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'include_dirs': [
     '..',
   ],
   'defines': [
     'SYNC_IMPLEMENTATION',
   ],
   'dependencies': [
     '../base/base.gyp:base',
     '../jingle/jingle.gyp:jingle_glue',
     '../jingle/jingle.gyp:notifier',
     '../third_party/cacheinvalidation/cacheinvalidation.gyp:cacheinvalidation',
     # TODO(akalin): Remove this (http://crbug.com/133352).
     '../third_party/cacheinvalidation/cacheinvalidation.gyp:cacheinvalidation_proto_cpp',
     '../third_party/libjingle/libjingle.gyp:libjingle',
   ],
   'export_dependent_settings': [
     '../jingle/jingle.gyp:notifier',
     '../third_party/cacheinvalidation/cacheinvalidation.gyp:cacheinvalidation',
   ],
   'sources': [
+    'notifier/ack_handler.cc',
+    'notifier/ack_handler.h',
+    'notifier/dropped_invalidation_tracker.cc',
+    'notifier/dropped_invalidation_tracker.h',
     'notifier/invalidation_handler.h',
     'notifier/invalidation_state_tracker.cc',
     'notifier/invalidation_state_tracker.h',
     'notifier/invalidation_util.cc',
     'notifier/invalidation_util.h',
     'notifier/unacked_invalidation_set.cc',
     'notifier/unacked_invalidation_set.h',
     'notifier/invalidator.h',
     'notifier/invalidator_registrar.cc',
     'notifier/invalidator_registrar.h',
@@ skipping 21 matching lines @@
         'notifier/registration_manager.h',
         'notifier/state_writer.h',
         'notifier/sync_invalidation_listener.cc',
         'notifier/sync_invalidation_listener.h',
         'notifier/sync_system_resources.cc',
         'notifier/sync_system_resources.h',
       ],
     }],
   ],
 }