BUG=398337

ANGLE_instanced_arrays defines the behavior of the non-instanced
draw calls (glDrawArrays, glDrawElements) such that they behave as
single-instance draws, so the vertex divisor should still apply. We
were handling this correctly in D3D11, but not D3D9.

This fixes a new WebGL conformance test:
https://www.khronos.org/registry/webgl/sdk/tests/conformance/extensions/angle-instanced-arrays.html

Change-Id: Ib50e189d866d6dc97612e46460db4ca1723b3662
Reviewed-on: https://chromium-review.googlesource.com/211445Tested-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>