[LayoutNG] Fix crash when hit-testing flow control text fragments

Bug: 866556
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: Ie9977ebaa733e43d54fa6006e88adb3fce7cfb50
Reviewed-on: https://chromium-review.googlesource.com/1146882
Reviewed-by: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578372}
2 files changed