Remove focus if supportsFocus state is changed.

Changes of *[tabindex], a[href], button[disabled], etc. affect focusable state,
but these changes don't always trigger layout. We need to ask focus check
explicitly.

BUG=265832

Review URL: https://chromiumcodereview.appspot.com/21055009

git-svn-id: svn://svn.chromium.org/blink/trunk@155336 bbb929c8-8fbe-4397-9dbb-9b2b20218538