Fixes the Quick Open integration test (#2696).

Note that I did sometimes see failures, but these appeared to be
genuine failures (as in the scroll position was not correct in the
window on screen).
Make the test more resilient with a wider band.

Rather than +/- 1 on the offset, use 40%-60% of the height.
remove extraneous comment.
Merge pull request #3415 from adobe/dangoor/2696-once-and-for-all

Fixes the Quick Open integration test (#2696).