This prints the current v8-specific processes on linux whenever the
test driver emits a heart beat (i.e. no output for 30 seconds).

This is to investigate the cause of currently hanging tests on linux.

Bug: v8:9145
Change-Id: I857bb6d1c5f0b0917c64cdc0aa6076c6633f9dd6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1578438
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60941}