Code review comment for lp:~dandrader/frame/smarter_backend

* The Window class no longer needs to subclass std::enable_shared_from_this<Window>.

* Any functions that may fail need to return a UFStatus and provide the return result through a referenced parameter. All of the new functions here should do this. I forgot about this when I approved the previous merge proposal as well. We should go back and fix these up.

* There's a stray newline at the end of UFFrame::GetSharedTouchById.

Everything else looks good :). This should really help backend implementations get things right the first time.