Implement minlength for <input> and <textarea>.
Add layout tests to test minlength behavior and new tooShort validity property. Enrich maxlength/tooLong layout tests while at it.

BUG=390485

Review URL: https://codereview.chromium.org/435753003

git-svn-id: svn://svn.chromium.org/blink/trunk@183454 bbb929c8-8fbe-4397-9dbb-9b2b20218538