Linux: fix getting termination status for known dead processes.

Linux: fix getting termination status for known dead processes.

While a process is being destroyed by the kernel, it will loose
its IPC file descriptors which signals to the browser that the process is dead.

In that timeframe, doing a non blocking waitpid() is racy and
can indicate the process as still being running while the kernel is
still destroying it.

We unify Linux with OS X and use known_dead even in the non Zygote case.

BUG=332635
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=244069

[jln (very slow on Chromium), 2014-01-09 03:37:21]

Antoine, this is what I had in mind until we address crbug.com/332522

I did manually check that kill -SEGV <pid_of_gpu_process> yields
TERMINATION_STATUS_PROCESS_CRASHED.

[piman, 2014-01-09 03:40:53]

LGTM. That's essentially what I came up with too. Having this in trunk should
help us identify the source of these crashes (if it's killed e.g. by the session
manager vs if it's a real crash).

[commit-bot: I haz the power, 2014-01-09 23:22:19]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jln@chromium.org/130633002/1

[commit-bot: I haz the power, 2014-01-10 01:05:33]

Retried try job too often on linux_aura for step(s) interactive_ui_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_aura...

[commit-bot: I haz the power, 2014-01-10 01:24:32]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jln@chromium.org/130633002/1

[commit-bot: I haz the power, 2014-01-10 03:26:32]

Change committed as 244069