[introspection] Add missing annotations to GDataDownloadStream
[introspection] Add missing annotations to GDataDownloadStream

Pecisk/libgdata-gtasks,pwithnall/libgdata,Pecisk/libgdata,Distrotech/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,Distrotech/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,GNOME/libgdata,Distrotech/libgdata,pwithnall/libgdata