It seems that DWM will, when given an HWND that has an associated
FlipEX swap chain, stretch the contents of the HWND to fill the new
window IF you don't issue draw calls to that HWND before the WM_PAINT
returns. This leads to horrendous sizing artifacts.

For Chromium, this is a show stopper.

But, FlipEx is definitely a good thing, for regular single process
applications.

So, is there a clean way to conditionally disable FlipEX for
these problem cases? The heuristic in this patch basically says "if your hwnd
is not in-process, then you're probably not painting in its HWND, so don't sue
FlipEX."

This catches the Chromium use case. There is still the possibility of a regular
single-process EGL application that tries to draw outside WM_PAINT that would
experience sizing artefacts. But, maybe that's OK.

Anyways, I'm not married to this technique. Just throwing something out there
to start the discussion. :)

Review URL: http://codereview.appspot.com/4536102

git-svn-id: https://angleproject.googlecode.com/svn/trunk@668 736b8ea6-26fd-11df-bfd4-992fa37f6226