Fix free memory calculation.

base/sys_info.h

 // Copyright (c) 2012 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_SYS_INFO_H_
 #define BASE_SYS_INFO_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 10 matching lines @@
 class BASE_EXPORT SysInfo {
  public:
   // Return the number of logical processors/cores on the current machine.
   static int NumberOfProcessors();
 
   // Return the number of bytes of physical memory on the current machine.
   static int64_t AmountOfPhysicalMemory();
 
   // Return the number of bytes of current available physical memory on the
   // machine.
+  // (The amount of memory that can be allocated without any significant
+  // impact on the system. It can lead to freeing inactive file-backed
+  // and/or speculative file-backed memory).
   static int64_t AmountOfAvailablePhysicalMemory();
 
   // Return the number of bytes of virtual memory of this process. A return
   // value of zero means that there is no limit on the available virtual
   // memory.
   static int64_t AmountOfVirtualMemory();
 
   // Return the number of megabytes of physical memory on the current machine.
   static int AmountOfPhysicalMemoryMB() {
     return static_cast<int>(AmountOfPhysicalMemory() / 1024 / 1024);
@@ skipping 104 matching lines @@
 
   // Returns true if this is a low-end device.
   // Low-end device refers to devices having less than 512M memory in the
   // current implementation.
   static bool IsLowEndDevice();
 };
 
 }  // namespace base
 
 #endif  // BASE_SYS_INFO_H_