Expose navigator.product and navigator.appCodeName constants to workers

Expose navigator.product and navigator.appCodeName constants to web workers as
well, as per the specification:
http://www.whatwg.org/specs/web-apps/current-work/multipage/workers.html#workernavigator
http://www.whatwg.org/specs/web-apps/current-work/multipage/timers.html#navigatorid

BUG=276316

Review URL: https://chromiumcodereview.appspot.com/22866014

git-svn-id: svn://svn.chromium.org/blink/trunk@157679 bbb929c8-8fbe-4397-9dbb-9b2b20218538