Pass 0 for the sample count to RenderTarget when there is no multisampling. BUG=angle:520 Change-Id: Idc9a19ece620d107b87110dac8e1ef7a24f565cc Reviewed-on: https://chromium-review.googlesource.com/228551 Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>