The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/505ab0512136f9b13c025775030c58fcb2d8a7a6

commit 505ab0512136f9b13c025775030c58fcb2d8a7a6
Author: Stefan Zager <szager@chromium.org>
Date: Wed Sep 12 03:13:26 2018

[IntersectionObserver] Support hit testing visual overflow

An element can be occluded by the visual overflow of another element,
for example if the occluding element has CSS box-shadow or
text-shadow. Add support for hit testing objects' visual overflow,
and use it in HitTestForOcclusion.

Also, make sure that the intersection observer algorithm is scheduled
to run when visual overflow changes.

BUG=878611
R=chrishtr@chromium.org

Change-Id: I9d65802e016a6d1b73f3398cf3054be5044d586f
Reviewed-on: https://chromium-review.googlesource.com/1212452
Commit-Queue: Stefan Zager <szager@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590584}
[add] https://crrev.com/505ab0512136f9b13c025775030c58fcb2d8a7a6/third_party/WebKit/LayoutTests/intersection-observer/v2/box-shadow.html
[add] https://crrev.com/505ab0512136f9b13c025775030c58fcb2d8a7a6/third_party/WebKit/LayoutTests/intersection-observer/v2/text-shadow.html
[modify] https://crrev.com/505ab0512136f9b13c025775030c58fcb2d8a7a6/third_party/blink/renderer/core/layout/hit_test_request.h
[modify] https://crrev.com/505ab0512136f9b13c025775030c58fcb2d8a7a6/third_party/blink/renderer/core/layout/layout_block.cc
[modify] https://crrev.com/505ab0512136f9b13c025775030c58fcb2d8a7a6/third_party/blink/renderer/core/layout/layout_box.cc
[modify] https://crrev.com/505ab0512136f9b13c025775030c58fcb2d8a7a6/third_party/blink/renderer/core/layout/layout_object.cc