In https://chromium-review.googlesource.com/c/chromium/src/+/1063996, I added the functionality to output benchmark's stdout to a file. The try run on https://ci.chromium.org/buildbot/tryserver.chromium.perf/obbs_fyi/331 was failing.

At first, I couldn't reproduce this locally. Once I dig more into it, it turns out because the obbs_fyi bot use "--xvfb" flag, which trigger a slightly different code path. In particular, when xvfb flag is enabled on Linux, xvfb.run_executable() method recursively run xvfb.py (see https://cs.chromium.org/chromium/src/testing/xvfb.py?rcl=eb9f60d092af8ebfdce0a6e507bb7509460b1b2b&l=87) and doesn't pass stdoutfile param through with that recursive call.

I will make a change to make sure xvfb.run_executable(..) passes stdoutfile through in that case