Seems due to https://chromium-review.googlesource.com/1085554, which I'm reluctant to revert.

Actually going ahead with the revert.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/29a25b6ce1f99ce6e74d8fe2e87aa491f11f367b

commit 29a25b6ce1f99ce6e74d8fe2e87aa491f11f367b
Author: Mikel Astiz <mastiz@chromium.org>
Date: Tue Jul 17 09:07:01 2018

Revert "Add support for mid ligature positions"

This reverts commit 1e3235b397f5fd7e875ae1548ee2ce385cb22af8.

Reason for revert: suspect for breaking webkit_layout_tests on
Mac, e.g. test offset-from-point-complex-scripts.html.

Bug:  864405 

Original change's description:
> Add support for mid ligature positions
> 
> Makes XPositionForOffset and CharacterIndexForPosition support
> return results inside a ligature glyph (while still not breaking ZWJs)
> by using a character-based TextBreakIterator inside glyphs.
> 
> Bug:  473476 
> Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
> Change-Id: I723cc8ba081958ff2d470d3e73ead6cbe327cf60
> Reviewed-on: https://chromium-review.googlesource.com/1085554
> Reviewed-by: Emil A Eklund <eae@chromium.org>
> Reviewed-by: Koji Ishii <kojii@chromium.org>
> Reviewed-by: Dominik Röttsches <drott@chromium.org>
> Commit-Queue: Fernando Serboncini <fserb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#575496}

TBR=eae@chromium.org,kojii@chromium.org,drott@chromium.org,fserb@chromium.org

Change-Id: Id20c3aca9139d65e4187009e7ef7b45f87cceb5e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  473476 
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng;luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Reviewed-on: https://chromium-review.googlesource.com/1140073
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575587}
[add] https://crrev.com/29a25b6ce1f99ce6e74d8fe2e87aa491f11f367b/third_party/WebKit/LayoutTests/platform/linux/fast/overflow/image-selection-highlight-expected.txt
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