Update from https://crrev.com/328418

base/mac/memory_pressure_monitor_mac.h

Index: base/mac/memory_pressure_monitor_mac.h
diff --git a/base/mac/memory_pressure_monitor_mac.h b/base/mac/memory_pressure_monitor_mac.h
new file mode 100644
index 0000000000000000000000000000000000000000..aebdd6538e40b1c62b5b8d8bd3c9e573e7a6616a
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+++ b/base/mac/memory_pressure_monitor_mac.h
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+// 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 BASE_MEMORY_MEMORY_PRESSURE_MONITOR_MAC_H_
+#define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_MAC_H_
+
+#include <dispatch/dispatch.h>
+
+#include "base/base_export.h"
+#include "base/memory/memory_pressure_listener.h"
+#include "base/memory/memory_pressure_monitor.h"
+
+// The following was added to <dispatch/source.h> after 10.8.
+// TODO(shrike): Remove the DISPATCH_MEMORYPRESSURE_NORMAL ifndef once builders
+// reach 10.9 or higher.
+#ifndef DISPATCH_MEMORYPRESSURE_NORMAL
+
+#define DISPATCH_MEMORYPRESSURE_NORMAL    0x01
+#define DISPATCH_MEMORYPRESSURE_WARN      0x02
+#define DISPATCH_MEMORYPRESSURE_CRITICAL  0x04
+
+#endif  // DISPATCH_MEMORYPRESSURE_NORMAL
+
+namespace base {
+
+class TestMemoryPressureMonitorMac;
+
+struct DispatchSourceSDeleter {
+  void operator()(dispatch_source_s* ptr) {
+    dispatch_source_cancel(ptr);
+    dispatch_release(ptr);
+  }
+};
+
+// Declares the interface for the Mac MemoryPressureMonitor, which reports
+// memory pressure events and status.
+class BASE_EXPORT MemoryPressureMonitorMac : public MemoryPressureMonitor {
+ public:
+  using MemoryPressureLevel = base::MemoryPressureListener::MemoryPressureLevel;
+  MemoryPressureMonitorMac();
+  ~MemoryPressureMonitorMac() override;
+
+  // Returns the currently-observed memory pressure.
+  MemoryPressureLevel GetCurrentPressureLevel() const override;
+
+ private:
+  friend TestMemoryPressureMonitorMac;
+
+  static MemoryPressureLevel
+      MemoryPressureLevelForMacMemoryPressure(int mac_memory_pressure);
+  static void NotifyMemoryPressureChanged(dispatch_source_s* event_source);
+
+  scoped_ptr<dispatch_source_s, DispatchSourceSDeleter>
+      memory_level_event_source_;
+
+  DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitorMac);
+};
+
+}  // namespace base
+
+#endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_MAC_H_