Add Mac memory pressure statistic reporting and consolidate platform code

base/memory/memory_pressure_monitor_chromeos.h

 // Copyright 2014 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_CHROMEOS_H_
 #define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_
 
 #include "base/base_export.h"
 #include "base/files/scoped_file.h"
 #include "base/macros.h"
@@ skipping 83 matching lines @@
       current_memory_pressure_level_;
 
   // A periodic timer to check for resource pressure changes. This will get
   // replaced by a kernel triggered event system (see crbug.com/381196).
   base::RepeatingTimer timer_;
 
   // To slow down the amount of moderate pressure event calls, this counter
   // gets used to count the number of events since the last event occured.
   int moderate_pressure_repeat_count_;
 
+  // The "Memory.PressureLevel" statistic is recorded every
+  // 5 seconds, but the timer to report "ChromeOS.MemoryPressureLevel"
+  // fires every second. This counter is used to allow reporting
+  // "Memory.PressureLevel" correctly without adding another
+  // timer.
+  int seconds_since_reporting_;
+
   // The thresholds for moderate and critical pressure.
   const int moderate_pressure_threshold_percent_;
   const int critical_pressure_threshold_percent_;
 
   // File descriptor used to detect low memory condition.
   ScopedFD low_mem_file_;
 
   DispatchCallback dispatch_callback_;
 
   base::WeakPtrFactory<MemoryPressureMonitor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
 };
 
 }  // namespace chromeos
 }  // namespace base
 
 #endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_CHROMEOS_H_