fast/forms/search-event-delay.html is asserting in markAllMisspellingsAndBadGrammarIn...

fast/forms/search-event-delay.html is asserting in markAllMisspellingsAndBadGrammarInRanges()
https://bugs.webkit.org/show_bug.cgi?id=82761

Reviewed by Ryosuke Niwa.

Speculative fix for this assertion: have InternalSettings save
and restore the value of the "unifiedTextCheckerEnabled" setting
between tests, so that tests change the value of this setting don't
affect later tests.

* testing/InternalSettings.cpp:
(WebCore::InternalSettings::Backup::Backup):
(WebCore::InternalSettings::Backup::restoreTo):
* testing/InternalSettings.h:
(Backup):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@128941 268f45cc-cd09-0410-ab3c-d52691b4dbfc