Add SyncAuthProvider interface and implementation

sync/sync_internal_api.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',
@@ skipping 89 matching lines @@
     'internal_api/public/sessions/model_neutral_state.cc',
     'internal_api/public/sessions/model_neutral_state.h',
     'internal_api/public/sessions/status_counters.cc',
     'internal_api/public/sessions/status_counters.h',
     'internal_api/public/sessions/sync_session_snapshot.cc',
     'internal_api/public/sessions/sync_session_snapshot.h',
     'internal_api/public/sessions/type_debug_info_observer.cc',
     'internal_api/public/sessions/type_debug_info_observer.h',
     'internal_api/public/sessions/update_counters.cc',
     'internal_api/public/sessions/update_counters.h',
+    'internal_api/public/sync_auth_provider.h',
     'internal_api/public/sync_core_proxy.h',
     'internal_api/public/sync_encryption_handler.cc',
     'internal_api/public/sync_encryption_handler.h',
     'internal_api/public/sync_manager.cc',
     'internal_api/public/sync_manager.h',
     'internal_api/public/sync_manager_factory.h',
     'internal_api/public/user_share.h',
     'internal_api/public/util/experiments.h',
     'internal_api/public/util/immutable.h',
     'internal_api/public/util/report_unrecoverable_error_function.h',
@@ skipping 28 matching lines @@
     'internal_api/sync_rollback_manager_base.h',
     'internal_api/syncapi_internal.cc',
     'internal_api/syncapi_internal.h',
     'internal_api/syncapi_server_connection_manager.cc',
     'internal_api/syncapi_server_connection_manager.h',
     'internal_api/user_share.cc',
     'internal_api/write_node.cc',
     'internal_api/write_transaction.cc',
   ],
 }