Implement reportValidity()

BUG=390486
TEST=Added layout tests based on checkValidity tests, with added focus check

Review URL: https://codereview.chromium.org/660783002

git-svn-id: svn://svn.chromium.org/blink/trunk@184177 bbb929c8-8fbe-4397-9dbb-9b2b20218538