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

components/arc/metrics/arc_metrics_service.cc

 // 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.
 
 #include "components/arc/metrics/arc_metrics_service.h"
 
 #include <string>
 #include <utility>
 
 #include "base/logging.h"
@@ skipping 10 matching lines @@
 const char kBootProgressEnableScreen[] = "boot_progress_enable_screen";
 
 }  // namespace
 
 namespace arc {
 
 ArcMetricsService::ArcMetricsService(ArcBridgeService* bridge_service)
     : ArcService(bridge_service),
       binding_(this),
       process_observer_(this),
+      oom_kills_monitor_handle_(OomKillsMonitor::StartMonitoring()),
       weak_ptr_factory_(this) {
   arc_bridge_service()->metrics()->AddObserver(this);
   arc_bridge_service()->process()->AddObserver(&process_observer_);
-  oom_kills_monitor_.Start();
 }
 
 ArcMetricsService::~ArcMetricsService() {
   DCHECK(CalledOnValidThread());
   arc_bridge_service()->process()->RemoveObserver(&process_observer_);
   arc_bridge_service()->metrics()->RemoveObserver(this);
 }
 
 bool ArcMetricsService::CalledOnValidThread() {
   // Make sure access to the Chrome clipboard is happening in the UI thread.
@@ skipping 125 matching lines @@
 
 void ArcMetricsService::ProcessObserver::OnInstanceReady() {
   arc_metrics_service_->OnProcessInstanceReady();
 }
 
 void ArcMetricsService::ProcessObserver::OnInstanceClosed() {
   arc_metrics_service_->OnProcessInstanceClosed();
 }
 
 }  // namespace arc