[Storage] Add type signature to `readall`
@@ -510,6 +510,7 @@ class StorageStreamDownloader(object): # pylint: disable=too-many-instance-attr
chunk_size=self._config.max_chunk_get_size)
def readall(self):
+ # type: () -> Union[bytes, str]
"""Download the contents of this blob.
This operation is blocking until all data is downloaded.
