commitcloud: add extras method to FakeCtx

Summary:
The `snapshot` extension expects to be able to call `extra()` on the smartlog
context, so make the method available.

Reviewed By: quark-zju

Differential Revision: D18456550

fbshipit-source-id: 9d1620e1b5fbb0866e728c7b378d37b4de9dbe21

edenscm/hgext/commitcloud/baseservice.py

@@ -82,6 +82,9 @@ class FakeCtx(object):
     def date(self):
         return (self._nodeinfo.date, 0)
 
+    def extra(self):
+        return {}
+
 
 def topological(graph):
     tovisit = sorted(graph.keys())