The test fails with the following at a very low flake rate:
../../third_party/angle/src/tests/gl_tests/VertexAttributeTest.cpp:230: Failure
Expected equality of these values:
  angle::MakeGLColor(255, 255, 255, 255)
    Which is: White
  angle::ReadColor((midPixelX + viewportSize[2]) / 2, midPixelY)
    Which is: Transparent Black

TBR=jmadill@chromium.org
Bug: angleproject:4269
Change-Id: I82752acfbcb2a067ccb35a7a456def03299c359f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1987258Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>