[Telemetry] Terminate any dangling subprocesses

This is designed to prevent deadlocks on the buildbots.

I couldn't figure out a way to kill them without killing the parent as well. I
also haven't looked into a Windows equivalent yet.

BUG=357059

Review URL: https://codereview.chromium.org/301313007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274036 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed