Integrate Controller w/ AttachmentDownloadService

* Add ControllerService to Controller and call this from
  AttachmentDownloadService to handle attachment loading

(It's a redo of I3a6c2a40.  Submitting for mlbank, who had a trouble
with repo.)

Change-Id: I7c90761ec4e213d6dc331fc894c7b77e84ad43a6
1 file changed