Print some output in long perf tests, to keep them alive
Print some output in long perf tests, to keep them alive

At least Android try bots seem to have a timeout that will forcibly shut
down the executable if no output has been observed for 60s. Since full
stack test typically run for 60s we need to output give some to avoid
racy shutdown.

BUG=chromium:513170
R=pbos@webrtc.org

Review URL: https://codereview.webrtc.org/1288453003 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9822}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 2c27430545098f17bc716335a8677a9d21cecac0

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