Consolidate code monitoring low memory kills and OOM kills to MemoryKillsMonitor on ChromeOS.

components/arc/metrics/oom_kills_monitor.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_OOM_KILLS_MONITOR_H_
-#define COMPONENTS_ARC_METRICS_OOM_KILLS_MONITOR_H_
-
-#include <memory>
-
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/synchronization/atomic_flag.h"
-#include "base/threading/simple_thread.h"
-
-namespace arc {
-
-// Traces kernel OOM kill events and lowmemorykiller (if enabled) events.
-//
-// OomKillsMonitor listens to kernel messages for both OOM kills and
-// lowmemorykiller kills, then reports to UMA. It uses a non-joinable thread
-// in order to avoid blocking shutdown.
-//
-// Note: There should be only one OomKillsMonitor instance globally at any given
-// time, otherwise UMA would receive duplicate events.
-class OomKillsMonitor : public base::DelegateSimpleThread::Delegate {
- public:
-  // A handle representing the OomKillsMonitor's lifetime (the monitor itself
-  // can't be destroyed per being a non-joinable Thread).
-  class Handle {
-   public:
-    // Constructs a handle that will flag |outer| as shutting down on
-    // destruction.
-    explicit Handle(OomKillsMonitor* outer);
-
-    ~Handle();
-
-   private:
-    OomKillsMonitor* const outer_;
-  };
-
-  // Instantiates the OomKillsMonitor instance and starts it. This must only
-  // be invoked once per process.
-  static Handle StartMonitoring();
-
- private:
-  OomKillsMonitor();
-  ~OomKillsMonitor() override;
-
-  // Overridden from base::DelegateSimpleThread::Delegate:
-  void Run() override;
-
-  // A flag set when OomKillsMonitor is shutdown so that its thread can poll
-  // it and attempt to wind down from that point (to avoid unnecessary work, not
-  // because it blocks shutdown).
-  base::AtomicFlag is_shutting_down_;
-
-  // The underlying worker thread which is non-joinable to avoid blocking
-  // shutdown.
-  std::unique_ptr<base::DelegateSimpleThread> non_joinable_worker_thread_;
-
-  DISALLOW_COPY_AND_ASSIGN(OomKillsMonitor);
-};
-
-}  // namespace arc
-
-#endif  // COMPONENTS_ARC_METRICS_OOM_KILLS_MONITOR_H_