import: Move SubscriberHandler to import_util.

zerver/data_import/import_util.py

@@ -19,6 +19,20 @@ from zerver.lib.parallel import run_parallel
 # stubs
 ZerverFieldsT = Dict[str, Any]
 
+class SubscriberHandler:
+    def __init__(self) -> None:
+        self.stream_info = dict()  # type: Dict[int, Set[int]]
+
+    def set_info(self,
+                 stream_id: int,
+                 users: Set[int]) -> None:
+        self.stream_info[stream_id] = users
+
+    def get_users(self,
+                  stream_id: int) -> Set[int]:
+        users = self.stream_info[stream_id]
+        return users
+
 def build_zerver_realm(realm_id: int, realm_subdomain: str, time: float,
                        other_product: str) -> List[ZerverFieldsT]:
     realm = Realm(id=realm_id, date_created=time,