Added missing imports.
diff --git a/googleapiclient/discovery.py b/googleapiclient/discovery.py
index 598b222..c451b47 100644
--- a/googleapiclient/discovery.py
+++ b/googleapiclient/discovery.py
@@ -61,6 +61,8 @@
 from googleapiclient.errors import UnknownApiNameOrVersion
 from googleapiclient.errors import UnknownFileType
 from googleapiclient.http import BatchHttpRequest
+from googleapiclient.http import HttpMock
+from googleapiclient.http import HttpMockSequence
 from googleapiclient.http import HttpRequest
 from googleapiclient.http import MediaFileUpload
 from googleapiclient.http import MediaUpload