GitLab

Previously we used the *layout* viewport's rectangle to determine
if a certain node was visible or not. Let's use the *visual*
viewport instead. Now:

 A visible node is a node that intersects the visual viewport.

This logic is used by spatnav to rule out offscreen focus candidates
and an offscreen activeElement. When activeElement is offscreen,
spatnav doesn't use it as its search origin; the search will start
at an edge of the visual viewport instead.

For consistency, I replaced all other uses of LayoutViewport()
with GetScrollableArea() - even though fixing HasOffscreenRect()
was enough to fix Issue 823227.

Bug: 823227
Change-Id: I8a89cfc98d896998b899a5246f2c38e23fe0171b
Reviewed-on: https://chromium-review.googlesource.com/1204094
Commit-Queue: Hugo Holgersson <hugoh@vewd.com>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588792}