Perf Tests: Add stdout printing arg to bot mode. This can be useful for debugging and also for perf tests. The perf tests output gets scraped from stdout. Bug: angleproject:5124 Change-Id: Id5005df3f2b66be9497a9ba422abd47b95a1a330 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2486097 Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Commit-Queue: Jamie Madill <jmadill@chromium.org>