I'm struggling to see why it would take so long.
Webkit is (obviously) already running on OSX. The new Javascript engine should be platform agnostic (if not, someone should lose their job!). A competent programmer could put together a custom window class in a week.
Ok, "crash control" might be tricky, but other than that I really can't see why it would take even a month.
The source code is open and available. If you would be so kind as to knock it all out in a week then Google would appreciate the help and welcome your contributed code.