Add brightray_example::Window

This wrapper around a native window makes it easier to share code
between Windows and Mac. Right now this is only implemented on Mac;
Windows is next!
Stub out WindowWin

It doesn't do anything yet, but gets Windows compiling.

* vendor/brightray 0c775a7...76867b9 (2):
  > Only compile HandleKeyboardEvent on Mac
  > Merge pull request #17 from brightray/windows-brightray_example
Show a window on Windows

You can't show the dev tools, but other than that things seem to work!

* vendor/brightray 76867b9...fa15d36 (2):
  > Get libchromiumcontent back on master
  > Stub out InspectableWebContentsViewWin