[Sync] Register USS types with ModelTypeRegistry before download

sync/internal_api/sync_manager_impl.h

 // Copyright 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.
 
 #ifndef SYNC_INTERNAL_API_SYNC_MANAGER_IMPL_H_
 #define SYNC_INTERNAL_API_SYNC_MANAGER_IMPL_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 276 matching lines @@
   base::ObserverList<SyncManager::Observer> observers_;
 
   // The ServerConnectionManager used to abstract communication between the
   // client (the Syncer) and the sync server.
   scoped_ptr<SyncAPIServerConnectionManager> connection_manager_;
 
   // Maintains state that affects the way we interact with different sync types.
   // This state changes when entering or exiting a configuration cycle.
   scoped_ptr<ModelTypeRegistry> model_type_registry_;
 
-  // The main interface for non-blocking sync types and a thread-safe wrapper.
-  scoped_ptr<syncer_v2::SyncContext> sync_context_;
+  // Thread-safe wrapper for main interface for non-blocking sync types.
   scoped_ptr<syncer_v2::SyncContextProxy> sync_context_proxy_;
 
   // A container of various bits of information used by the SyncScheduler to
   // create SyncSessions.  Must outlive the SyncScheduler.
   scoped_ptr<sessions::SyncSessionContext> session_context_;
 
   // The scheduler that runs the Syncer. Needs to be explicitly
   // Start()ed.
   scoped_ptr<SyncScheduler> scheduler_;
 
@@ skipping 39 matching lines @@
   scoped_ptr<SyncEncryptionHandlerImpl> sync_encryption_handler_;
 
   base::WeakPtrFactory<SyncManagerImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncManagerImpl);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_SYNC_MANAGER_IMPL_H_