[Sync] Add support for automatic enabling of syncing tab favicons.

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 139 matching lines @@
         'util/cryptographer.h',
 
         # TODO(akalin): Figure out a better place to put
         # data_encryption_win*; it's also used by autofill.
         'util/data_encryption_win.cc',
         'util/data_encryption_win.h',
 
         'util/data_type_histogram.h',
         'util/encryptor.h',
         'util/enum_set.h',
+        'util/experiments.h',
         'util/extensions_activity_monitor.cc',
         'util/extensions_activity_monitor.h',
         'util/get_session_name.cc',
         'util/get_session_name.h',
         'util/get_session_name_mac.mm',
         'util/get_session_name_mac.h',
         'util/get_session_name_win.cc',
         'util/get_session_name_win.h',
         'util/immutable.h',
         'util/logging.cc',
@@ skipping 455 matching lines @@
         '../net/net.gyp:net_test_support',
         'sync',
         'sync_notifier',
       ],
       'sources': [
         'tools/sync_listen_notifications.cc',
       ],
     },
   ],
 }