XSSAuditor bypass with framset tags.

BUG=291180
R=abarth@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23441066

git-svn-id: svn://svn.chromium.org/blink/trunk@157794 bbb929c8-8fbe-4397-9dbb-9b2b20218538