GitLab

When an object's fragments change, e.g.
- the object moved from one fragment to another fragment of the
  flow thread;
- the object resized and created more or less fragments
etc., we need to update paint properties of the subtree.

The new logic also covers the previous SetNeedsPaintPropertyUpdate
logic for multicols.

Bug: 817803
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: Ib641c1e5ef5af7d93b8fb8de70cdc9aae2382fc9
Reviewed-on: https://chromium-review.googlesource.com/953566Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542356}