Move OomKillsMonitor from a single-threaded SequencedWorkerPool to a non-joinable thread.

components/arc/metrics/arc_metrics_service.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H_
 #define COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread_checker.h"
@@ skipping 52 matching lines @@
 
     ArcMetricsService* arc_metrics_service_;
   };
 
   mojo::Binding<mojom::MetricsHost> binding_;
 
   ProcessObserver process_observer_;
   base::ThreadChecker thread_checker_;
   base::RepeatingTimer timer_;
 
-  OomKillsMonitor oom_kills_monitor_;
+  OomKillsMonitor::Handle oom_kills_monitor_handle_;
 
   base::TimeTicks arc_start_time_;
 
   // Always keep this the last member of this class to make sure it's the
   // first thing to be destructed.
   base::WeakPtrFactory<ArcMetricsService> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcMetricsService);
 };
 
 }  // namespace arc
 
 #endif  // COMPONENTS_ARC_METRICS_ARC_METRICS_SERVICE_H_