Starting from this build the test times out after 300s about two-thirds of the time https://build.chromium.org/p/chromium.gpu.fyi/builders/Mac%20Retina%20Release%20%28NVIDIA%29/builds/4396

When it doesn't time out the test takes 137s and succeeds. I haven't been able to find differences between the swarming slaves that time out and those who don't. In fact one of the slaves both timed out and succeeded so I'm not sure how to investigate further.