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>
 
 #include <map>
 #include <string>
 
 #include "base/base_export.h"
 #include "base/files/file_path.h"
+#include "base/gtest_prod_util.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 
 namespace base {
 
+namespace debug {
+FORWARD_DECLARE_TEST(SystemMetricsTest, ParseMeminfo);
+}
+
+struct SystemMemoryInfoKB;
+
 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 99 matching lines @@
   static std::string GetAndroidBuildID();
 
   static int DalvikHeapSizeMB();
   static int DalvikHeapGrowthLimitMB();
 #endif  // defined(OS_ANDROID)
 
   // 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();
+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(SysInfoTest, AmountOfAvailablePhysicalMemory);
+  FRIEND_TEST_ALL_PREFIXES(debug::SystemMetricsTest, ParseMeminfo);
+
+#if defined(OS_LINUX) || defined(OS_ANDROID)
+  static int64_t AmountOfAvailablePhysicalMemory(
+      const SystemMemoryInfoKB& meminfo);
+#endif
 };
 
 }  // namespace base
 
 #endif  // BASE_SYS_INFO_H_