[Sync] Add ProfileSyncService::GetModelTypeStoreFactory.

components/sync/model/model_type_store.h

Index: components/sync/model/model_type_store.h
diff --git a/components/sync/model/model_type_store.h b/components/sync/model/model_type_store.h
index d640c9eb5d78ac6032ff05173b33a0524748aa82..dfe9e3fa4f023fc1feb4719c6fe06e31f7d456cf 100644
--- a/components/sync/model/model_type_store.h
+++ b/components/sync/model/model_type_store.h
@@ -195,6 +195,10 @@ class ModelTypeStore {
   // It will delete all metadata records and global metadata record.
 };
 
+// Typedef for a store factory that has all params bound except InitCallback.
+using ModelTypeStoreFactory =
+    base::Callback<void(const ModelTypeStore::InitCallback&)>;
+
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_MODEL_TYPE_STORE_H_