This this was missed because it doesn't add its own enum value and
instead reuses GL_NONE.

Bug: chromium:976374
Test: chrome --enable-features=UseSkiaRenderer,UiGpuRasterization \
  --enable-gpu-rasterization \
  --enable-oop-rasterization \
  --use-vulkan=native \
  --use-gl=angle \
  --use-angle=vulkan

Change-Id: I73437211fef3253801e899cb6e50a8e18865cc65
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1665329
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>