commit 6a1372cf43d08a04223bae0d3a921e4658822421
author Philip Rogers <pdr@chromium.org> Tue Jan 15 23:59:28 2019
committer Commit Bot <commit-bot@chromium.org> Tue Jan 15 23:59:28 2019
tree a10e4fa4728c08d96295c8fbcfb2fd13df22507a
parent e21c19877108d278decc483c238d5c63f6e45c5f

Force piercing subtree update on scroll tree hierarchy changes

The scroll tree does not have isolation nodes so it is not safe to
early-out from property tree building if there is a scroll hierarchy
change. For example, imagine three nested scroll nodes: 1 - 2 - 3.
If (2) is deleted, (3)'s parent will still be (2) and needs to be
updated to point to (1). A scroll node can be deleted when a frame is
resized and is no longer scrollable. This patch forces a piercing
update, which does not early out, on scroll tree hierarchy changes.

A WPT test was not used because the added test requires the
prefer-compositing-to-lcd-text flag to crash. This is tested with:
virtual/prefer_compositing_to_lcd_text/compositing/overflow/nested-frame-overflow-crash.html

Bug: 921838
Change-Id: I98c108c127a4e59037b9096866e0bc14e1c558af
Reviewed-on: https://chromium-review.googlesource.com/c/1413065
Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622886}