D3D10 cards perform poorly when the pixel shader outputs to multiple
render targets that are not bound.

BUG=325581

Change-Id: I13f6f98861ffeb77cd21f7401ded4425e4ea7841
Reviewed-on: https://chromium-review.googlesource.com/185400Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/190341