Update from https://crrev.com/315085

base/chromeos/memory_pressure_observer_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_CHROMEOS_MEMORY_PRESSURE_OBSERVER_CHROMEOS_H_
 #define BASE_CHROMEOS_MEMORY_PRESSURE_OBSERVER_CHROMEOS_H_
 
 #include "base/base_export.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
@@ skipping 58 matching lines @@
 
   // Stop observing the memory fill level.
   // May be safely called if StartObserving has not been called.
   void StopObserving();
 
   // The function which gets periodically called to check any changes in the
   // memory pressure. It will report pressure changes as well as continuous
   // critical pressure levels.
   void CheckMemoryPressure();
 
+  // The function periodically checks the memory pressure changes and records
+  // the UMA histogram statistics for the current memory pressure level.
+  void CheckMemoryPressureAndRecordStatistics();
+
   // Get the memory pressure in percent (virtual for testing).
   virtual int GetUsedMemoryInPercent();
 
   // The current memory pressure.
   base::MemoryPressureListener::MemoryPressureLevel
       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<MemoryPressureObserverChromeOS> 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 thresholds for moderate and critical pressure.
   const int moderate_pressure_threshold_percent_;
   const int critical_pressure_threshold_percent_;
 
   base::WeakPtrFactory<MemoryPressureObserverChromeOS> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureObserverChromeOS);
 };
 
 }  // namespace base
 
 #endif  // BASE_CHROMEOS_MEMORY_PRESSURE_OBSERVER_CHROMEOS_H_