Convert editing/inserting/5156401-2.html with selection_test()

This patch converts the web test with selection_test() to promote the
usage of W3C test harness. It also avoid a minor 1px image diff with
bidi caret affinity in crrev.com/c/1419249.

Bug: 894651
Change-Id: Iee531e6f3f6bc939b9459768cffd213edaebeb5e
Reviewed-on: https://chromium-review.googlesource.com/c/1423220
Auto-Submit: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624522}
5 files changed