DOM.visualBounds now includes scrollbars

- While not ideal this fixes most (if not all) of the ScaleManager issue
  pointed out in #1400. This issue should be addressed later. As of now,
  as an interim fix, this avoids the reported issue entirely (or at least
  I have not been able to reproduce it), as well as assorted artifacts
  when resizign a window while scaling.

- The is is the 2.1 behavior: In certain cases this can result in the
  right or bottom of the Game being cut-off slightly (the width of a
  scrollbar) instead of scaled, which is why it was originally changed.