Make sure user can always get to next page with keyboard.

There's a case where hitting the left/right arrow in the first/last
column wouldn't give focus to an icon on the next page because it is
vertically too far from the first icon to be considered. This makes
for a bad user experience, because there is no way to switch pages
with the keyboard. So now we brute-force search for an appropriate
icon if none was found in this case.

Bug: 25434120
Change-Id: Ifdead0e3b458717ccb33e2f0ec7c15f1fcce4b95