Move OomKillsMonitor from a single-threaded SequencedWorkerPool to a non-joinable thread.
The semantics are equivalent after this CL:
- SequencedWorkerPool::CONTINUE_ON_SHUTDOWN => non-joinable thread + leaky instance.
- Actually, it's better than before because with lack of a Leaky lazy instance,
there was a join despite the CONTINUE_ON_SHUTDOWN request [1].
- Ramping worker thread down on destruction through OomKillsMonitorHandle.
Also, cleanup the SimpleThread::Options API, making it more like Thread::Options.
Non-joinable SimpleThreads will have to remain alive so long as their Run() method uses
member state (SimpleThread itself won't after invoking Run()).
DelegateSimpleThread provides a safe way to do this by explicitly supporting
being deleted while Run() is active but ensuring the Delegate itself outlives Run()).
Note: it might seem overkill to let DelegateSimpleThread be deleted early but this is
eventually what I want to do for base::Thread (https://crbug.com/629139#c14) and this
is a good precursor to this paradigm (it really takes all its sense on base::Thread where
the destructor is more meaningful though -- winds down the MessageLoop).
The logic on SimpleThread is fairly simple, the complexity is in the assertions (which
were put behind DCHECK_IS_ON() to clearly isolate them) and the tests.
Reason for revert:
Reference run still breaks when this is enabled.
Original issue's description:
> Re-enable smoothness.tough_filters_cases.reference on Android One.
>
> This is a manual revert of 8454ebfd9efc7418ed61e44a07947607418ab8c9.
>
> Now that we have a new reference build, this should be working again.
> If not, we'll disable again.
>
> <email address hidden>
> BUG=616520
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.perf:android_s5_perf_cq;master.tryserver.chromium.perf:linux_perf_cq;master.tryserver.chromium.perf:mac_retina_perf_cq;master.tryserver.chromium.perf:winx64_10_perf_cq
>
> Committed: https://crrev.com/e26768713260b6912d627639218ee1dcadd59364
> Cr-Commit-Position: refs/heads/master@{#411849}
<email address hidden>
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true BUG=616520
