GitLab

Split the behavior of left/right from up/down when focused on
thumbnails. The behavior of up/down stay the same, and they will only
change the focus to an adjacent thumbnail when pressed.

Left/right when focused on a thumbnail now also change the page of the
contents, regardless of the presence of a horizontal zoom bar on the
contents.

Additionally, when the page of the contents change while focused on a
thumbnail, the focus is forwarded to the thumbnail of the new most
visible page.

Bug: 652400
Change-Id: I4da7caadbf6eb25899f8f4091047727b3d719daa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438984Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812624}