Convert editing/spelling/spelling.html with spellcheck_test
This patch converts editing/spelling/spelling.html with spellcheck_test
as a preparation of implementing idle time spellchecker, and renames it
to spelling_after_newline.html to better summarize the test case.
BUG=
517298
Committed:
https://crrev.com/b85bedf0657d101dfbf37ff17094de5bc859433d
Cr-Commit-Position: refs/heads/master@{#427643}