[Sync] Convert SyncSessionSnapshot to a copy-able class.

sync/sync.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     # The core sync library.
@@ skipping 59 matching lines @@
         'engine/process_updates_command.cc',
         'engine/process_updates_command.h',
         'engine/resolve_conflicts_command.cc',
         'engine/resolve_conflicts_command.h',
         'engine/store_timestamps_command.cc',
         'engine/store_timestamps_command.h',
         'engine/syncer.cc',
         'engine/syncer.h',
         'engine/syncer_command.cc',
         'engine/syncer_command.h',
+        'engine/sync_engine_event.cc',
+        'engine/sync_engine_event.h',
         'engine/syncer_proto_util.cc',
         'engine/syncer_proto_util.h',
         'engine/sync_scheduler.cc',
         'engine/sync_scheduler.h',
-        'engine/syncer_types.cc',
         'engine/syncer_types.h',
         'engine/syncer_util.cc',
         'engine/syncer_util.h',
         'engine/syncproto.h',
         'engine/traffic_logger.cc',
         'engine/traffic_logger.h',
         'engine/traffic_recorder.cc',
         'engine/traffic_recorder.h',
         'engine/update_applicator.cc',
         'engine/update_applicator.h',
@@ skipping 529 matching lines @@
         '../net/net.gyp:net_test_support',
         'sync',
         'sync_notifier',
       ],
       'sources': [
         'tools/sync_listen_notifications.cc',
       ],
     },
   ],
 }