[USS] Change the place where SharedModelTypeProcessor got created

sync/internal_api/public/shared_model_type_processor.h

Index: sync/internal_api/public/shared_model_type_processor.h
diff --git a/sync/internal_api/public/shared_model_type_processor.h b/sync/internal_api/public/shared_model_type_processor.h
index db208708111363b1ebae08d107db1a7c67f63bc6..c459b3686d469f5256d1763600d0278d2adadd08 100644
--- a/sync/internal_api/public/shared_model_type_processor.h
+++ b/sync/internal_api/public/shared_model_type_processor.h
@@ -38,14 +38,11 @@ class SYNC_EXPORT SharedModelTypeProcessor : public ModelTypeProcessor,
   SharedModelTypeProcessor(syncer::ModelType type, ModelTypeService* service);
   ~SharedModelTypeProcessor() override;
 
-  typedef base::Callback<void(syncer::SyncError, scoped_ptr<ActivationContext>)>
-      StartCallback;
-
   // Called by the DataTypeController to gather additional information needed
   // before a CommitQueue object can be created for this model type. Once the
   // metadata has been loaded, the info is collected and given to |callback|.
   // Once called, this can only be called again if sync is disconnected.
-  void OnSyncStarting(StartCallback callback);
+  void OnSyncStarting(const ModelTypeService::StartCallback& callback);
 
   // Disconnect this processor from the sync engine. Change metadata will
   // continue being processed and persisted, but no commits can be made until
@@ -125,7 +122,7 @@ class SYNC_EXPORT SharedModelTypeProcessor : public ModelTypeProcessor,
   sync_pb::DataTypeState data_type_state_;
 
   // Stores the start callback in between OnSyncStarting() and ReadyToConnect().
-  StartCallback start_callback_;
+  ModelTypeService::StartCallback start_callback_;
 
   // Indicates whether the metadata has finished loading.
   bool is_metadata_loaded_;