ASSERTION FAILED: object->style()->overflowX() == object->style()->overflowY()

Overriding overflow values to VISIBLE if they are different.

BUG=362510

Review URL: https://codereview.chromium.org/235043003

git-svn-id: svn://svn.chromium.org/blink/trunk@171446 bbb929c8-8fbe-4397-9dbb-9b2b20218538