Swarming task: https://chromium-swarm.appspot.com/task?id=417ea8baeaea5a10&refresh=10&show_raw=1


The shard successfully runs 1077 tests. But the processes do not exit. This eventually causes the swarming task to error out, after swarming repeatedly cannot kill the lingering processes. 

Presumably this is caused by shutdown hangs, otherwise the tests wouldn't have successfully complete. We need a mechanism for investigation into these sorts of problems.