Add memory pressure monitor for Linux.

components/memory_pressure/direct_memory_pressure_calculator_linux.h

-// Copyright 2015 The Chromium Authors. All rights reserved.
+// 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_MEMORY_PRESSURE_DIRECT_MEMORY_PRESSURE_CALCULATOR_WIN_H_
-#define COMPONENTS_MEMORY_PRESSURE_DIRECT_MEMORY_PRESSURE_CALCULATOR_WIN_H_
+#ifndef COMPONENTS_MEMORY_PRESSURE_DIRECT_MEMORY_PRESSURE_CALCULATOR_LINUX_H_
+#define COMPONENTS_MEMORY_PRESSURE_DIRECT_MEMORY_PRESSURE_CALCULATOR_LINUX_H_
 
 #include "components/memory_pressure/memory_pressure_calculator.h"
 
+#include "base/files/scoped_file.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "base/process/process_metrics.h"
-#include "build/build_config.h"
+#include "base/timer/timer.h"
 
 namespace memory_pressure {
 
-#if defined(MEMORY_PRESSURE_IS_POLLING)
-
 // OS-specific implementation of MemoryPressureCalculator. This is only defined
 // and used on platforms that do not have native memory pressure signals
 // (ChromeOS, Linux, Windows). OSes that do have native signals simply hook into
 // the appropriate subsystem (Android, Mac OS X).
 class DirectMemoryPressureCalculator : public MemoryPressureCalculator {
  public:
   // Exposed for unittesting. See .cc file for detailed discussion of these
   // constants.
-  static const int kLargeMemoryThresholdMb;
-  static const int kSmallMemoryDefaultModerateThresholdMb;
-  static const int kSmallMemoryDefaultCriticalThresholdMb;
-  static const int kLargeMemoryDefaultModerateThresholdMb;
-  static const int kLargeMemoryDefaultCriticalThresholdMb;
+  static const int kDefaultModerateThresholdPc;
+  static const int kDefaultCriticalThresholdPc;
 
   // Default constructor. Will choose thresholds automatically based on the
   // actual amount of system memory installed.
   DirectMemoryPressureCalculator();
 
   // Constructor with explicit memory thresholds. These represent the amount of
   // free memory below which the applicable memory pressure state applies.
   DirectMemoryPressureCalculator(int moderate_threshold_mb,
                                  int critical_threshold_mb);
 
@@ skipping 18 matching lines @@
 
   // Threshold amounts of available memory that trigger pressure levels. See
   // memory_pressure_monitor_win.cc for a discussion of reasonable values for
   // these.
   int moderate_threshold_mb_;
   int critical_threshold_mb_;
 
   DISALLOW_COPY_AND_ASSIGN(DirectMemoryPressureCalculator);
 };
 
-#endif  // defined(MEMORY_PRESSURE_IS_POLLING)
-
 }  // namespace memory_pressure
 
-#endif  // COMPONENTS_MEMORY_PRESSURE_DIRECT_MEMORY_PRESSURE_CALCULATOR_WIN_H_
+#endif  // COMPONENTS_MEMORY_PRESSURE_DIRECT_MEMORY_PRESSURE_CALCULATOR_LINUX_H_