Bug 1051061 - [VerticalHomescreen] TypeError: this.grid._grid.dragdrop is undefined

https://bugzilla.mozilla.org/show_bug.cgi?id=1051061
this test confused me at first because it does not have any assertions. But I guess if handleEvent() fails with an exception that will cause a failure, right?  Do you want to make that explicit with an assert.doesNotThrow() or something?  Or just a comment?