Create base::win::MemoryPressureMonitor class.

base/memory/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 BASE_MEMORY_MEMORY_PRESSURE_MONITOR_H_
 #define BASE_MEMORY_MEMORY_PRESSURE_MONITOR_H_
 
 #include "base/base_export.h"
 #include "base/memory/memory_pressure_listener.h"
 
 namespace base {
 
 // 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 BASE_EXPORT MemoryPressureMonitor {
  public:
   using MemoryPressureLevel = base::MemoryPressureListener::MemoryPressureLevel;
 
+  // Exposed for use with scoped_ptr.

[grt (UTC plus 2), 2015/05/06 13:26:36]

the fact that you need this for scoped_ptr at the moment is an implementation
detail and is subject to change, so i wouldn't mention it here in a comment. at
a higher level, the dtor must be virtual and public for the sake of polymorphism
so that derived types can have an "is a" relationship with the base class and be
passed around as such. i don't think this needs to be mentioned in a comment,
though, so just remove the comment here.

[chrisha, 2015/05/06 15:09:57]

Done.

+  virtual ~MemoryPressureMonitor();
+
   // Return the singleton MemoryPressureMonitor.
   static MemoryPressureMonitor* Get();
 
   // Returns the currently observed memory pressure.
   virtual MemoryPressureLevel GetCurrentPressureLevel() const = 0;
 
  protected:
   MemoryPressureMonitor();
-  virtual ~MemoryPressureMonitor();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MemoryPressureMonitor);
 };
 
 }  // namespace base
 
 #endif  // BASE_MEMORY_MEMORY_PRESSURE_MONITOR_H_