tree dafbf04753650434e347880a90ca0ede93cde553
parent 1562100299e04d7550e1eb03073caa5ddb2b9ec2
author Javier Fernández García-Boente <jfernandez@igalia.com> 1606918932 -0800
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> 1606920036 -0800

Adjust the part_start when the ShapeResultView is RTL

When creating a new ShapeResultView under RTL mode, the segments
process in the ShapeResultView::AddSegments are passed in reverse order.
This implies that the in case of multiple parts, the first RunInfoPart
may have an offset_ bigger than the start_index_.

When creating a new ShapeResultView instance from the one described
above as source, like we do in the NGLineBreaker::TruncateLineEndResult,
we will use the source's run that were placed in reverse order. We are
determining the part_start of this first RunInfoPart for the new result
based on the the start_index_ of the source's first run. We'll then
calculate the run_start based on this part_start value, subtracting
the above mentioned run's offset_.

However, as we stated before, in case of a source result under RTL
and multiple results, this offset_ value will be greater than the
start_index_, leading to a possible arithmetic overflow when
computing the run_start value.

Bug: 1152387
Change-Id: Ic69740497543b1d2d4dd8bf20d3f1b6c5de46bcc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567215
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832795}