Migrate ChromeOS to base::MemoryPressureMonitor

content/public/common/memory_pressure_monitor.h

+// Copyright 2015 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 CONTENT_PUBLIC_COMMON_MEMORY_PRESSURE_MONITOR_H_
+#define CONTENT_PUBLIC_COMMON_MEMORY_PRESSURE_MONITOR_H_
+
+#include "base/memory/memory_pressure_listener.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// Declares the interface for a MemoryPressureMonitor. There are multiple
+// OS specific implementations of this class. An instance of the memory
+// pressure observer is created at the process level, tracks memory usage, and
+// pushes memory state change notifications to the static function
+// base::MemoryPressureListener::NotifyMemoryPressure. This is turn notifies
+// all MemoryPressureListener instances via a callback.
+class CONTENT_EXPORT MemoryPressureMonitor {
+ public:
+  using MemoryPressureLevel = base::MemoryPressureListener::MemoryPressureLevel;
+
+  // Return the singleton MemoryPressureMonitor.
+  static MemoryPressureMonitor* Get();
+
+  // Returns the currently observed memory pressure.
+  virtual MemoryPressureLevel GetCurrentPressureLevel() const = 0;
+
+  // If the implementation is polling based forces an early evaluation of the
+  // memory pressure level. This allows for a tighter feedback loop when under
+  // critical memory pressure. If the implementation is not polling based this
+  // is a nop.
+  virtual void ScheduleEarlyCheck() = 0;
+
+ protected:
+  MemoryPressureMonitor();
+  virtual ~MemoryPressureMonitor();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_COMMON_MEMORY_PRESSURE_MONITOR_H_