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 41 matching lines @@
     'internal_api/public/base/enum_set.h',
     'internal_api/public/base/enum_set.h',
     'internal_api/public/base/invalidation.cc',
     'internal_api/public/base/invalidation.h',
     'internal_api/public/base/model_type.h',
     'internal_api/public/base/node_ordinal.cc',
     'internal_api/public/base/node_ordinal.h',
     'internal_api/public/base/ordinal.h',
     'internal_api/public/base/progress_marker_map.cc',
     'internal_api/public/base/progress_marker_map.h',
+    'internal_api/public/base/sync_auth_provider.h',
     'internal_api/public/base/unique_position.cc',
     'internal_api/public/base/unique_position.h',
     'internal_api/public/base_node.h',
     'internal_api/public/base_transaction.h',
     'internal_api/public/change_record.h',
     'internal_api/public/configure_reason.h',
     'internal_api/public/data_type_association_stats.cc',
     'internal_api/public/data_type_association_stats.h',
     'internal_api/public/data_type_debug_info_listener.cc',
     'internal_api/public/data_type_debug_info_listener.h',
@@ skipping 56 matching lines @@
     'internal_api/sync_core.h',
     'internal_api/sync_core_proxy.cc',
     'internal_api/sync_core_proxy_impl.cc',
     'internal_api/sync_core_proxy_impl.h',
     'internal_api/sync_encryption_handler_impl.cc',
     'internal_api/sync_encryption_handler_impl.h',
     'internal_api/sync_manager_factory.cc',
     'internal_api/sync_manager_impl.cc',
     'internal_api/sync_manager_impl.h',
     'internal_api/sync_rollback_manager_base.cc',
-    'internal_api/sync_rollback_manager_base.h',    
+    'internal_api/sync_rollback_manager_base.h',
     'internal_api/sync_rollback_manager.cc',
-    'internal_api/sync_rollback_manager.h',    
+    'internal_api/sync_rollback_manager.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',
   ],
 }