Use mojo to connect to BackgroundSyncManager object

content/content_child.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.
 
 {
   'dependencies': [
     '../base/base.gyp:base',
     '../components/mime_util/mime_util.gyp:mime_util',
     '../components/tracing.gyp:tracing',
     '../components/webcrypto/webcrypto.gyp:webcrypto',
@@ skipping 28 matching lines @@
     'private_child_sources': [
       'child/appcache/appcache_backend_proxy.cc',
       'child/appcache/appcache_backend_proxy.h',
       'child/appcache/appcache_dispatcher.cc',
       'child/appcache/appcache_dispatcher.h',
       'child/appcache/appcache_frontend_impl.cc',
       'child/appcache/appcache_frontend_impl.h',
       'child/appcache/web_application_cache_host_impl.cc',
       'child/appcache/web_application_cache_host_impl.h',
       'child/assert_matching_enums.cc',
-      'child/background_sync/background_sync_provider_thread_proxy.cc',
-      'child/background_sync/background_sync_provider_thread_proxy.h',
       'child/background_sync/background_sync_provider.cc',
       'child/background_sync/background_sync_provider.h',
       'child/background_sync/background_sync_type_converters.cc',
       'child/background_sync/background_sync_type_converters.h',
       'child/blink_platform_impl.cc',
       'child/blink_platform_impl.h',
       'child/blob_storage/blob_consolidation.cc',
       'child/blob_storage/blob_consolidation.h',
       'child/browser_font_resource_trusted.cc',
       'child/browser_font_resource_trusted.h',
@@ skipping 280 matching lines @@
         'child/npapi/webplugin_delegate_impl_mac.mm',
       ],
     }],
     ['OS=="win"', {
       'sources!': [
         'child/npapi/webplugin_delegate_impl_aura.cc',
       ],
     }],
   ],
 }