Convert execCommand/unlink.html to use w3c test harness
This patch converts "execCommand/unlink.html" to use w3c test
harness with |assert_selection()| to simplify for code and improve code health.
This patch also updates |assert_selection()| to serialize selection correctly
when anchor node and focus node aren't |Text| node, and adds sanity check
for expected text.
This patch is a preparation of committing crrev.com/2001083002, Make
FrameSelection to track associated Document.
BUG=n/a
TEST=n/a; no behavior changes
Review-Url: https://codereview.chromium.org/2016173002
Cr-Commit-Position: refs/heads/master@{#396791}
3 files changed
