Let SyncBackupManager keep backup data in memory until shutdown. Only persist

sync/sync.gyp

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
 
   'includes': [
@@ skipping 335 matching lines @@
         'sessions/model_type_registry.h',
         'sessions/nudge_tracker.cc',
         'sessions/nudge_tracker.h',
         'sessions/status_controller.cc',
         'sessions/status_controller.h',
         'sessions/sync_session.cc',
         'sessions/sync_session.h',
         'sessions/sync_session_context.cc',
         'sessions/sync_session_context.h',
         'syncable/blob.h',
+        'syncable/deferred_on_disk_directory_backing_store.cc',
+        'syncable/deferred_on_disk_directory_backing_store.h',
         'syncable/dir_open_result.h',
         'syncable/directory.cc',
         'syncable/directory.h',
         'syncable/directory_backing_store.cc',
         'syncable/directory_backing_store.h',
         'syncable/directory_change_delegate.h',
         'syncable/entry.cc',
         'syncable/entry.h',
         'syncable/entry_kernel.cc',
         'syncable/entry_kernel.h',
@@ skipping 140 matching lines @@
         'proto_out_dir': 'sync/protocol',
         'cc_generator_options': 'dllexport_decl=SYNC_PROTO_EXPORT:',
         'cc_include': 'sync/protocol/sync_proto_export.h',
       },
       'includes': [
         '../build/protoc.gypi'
       ],
     },
   ],
 }