Tracking bug for removal of frameless app windows for Project Eraser.

There's a confusing branch in the class hierarchy of HWNDMessageHandlerDelegate to support frameless app windows, which makes behavior in HWNDMessageHandler more confusing (an already notorious class). Also apps with frames don't use this code, so it's hard to test.

No one I've asked has been able to think of a single chrome app that uses frameless windows other than gnubby. I'm sure there are some out there though, and they will suddenly have a native window frame around them (but otherwise will still work).

As an upper bound, app launches are at ~700K per day. That's already very low and frameless apps are a (likely small) fraction of that.