CompositorNativeWindow11's IsValidNativeWindow can only return true or
crash. If a user passes in an invalid window handle, ANGLE's D3D11
backend will always crash.

Ideally this window type would be exposed through an extension and
the user passes in an enum telling ANGLE that the window is an
ISpriteVisual instead of ANGLE trying to detect it from a void pointer.

Bug: chromium:1176118
Change-Id: Ia7568adcd929dcd9200c7da2d0a991da55e1e89a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2846800Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>