Fix free memory calculation.

base/process/process_metrics.h

Index: base/process/process_metrics.h
diff --git a/base/process/process_metrics.h b/base/process/process_metrics.h
index 2448a715ace9b5eade7f09524561ffcedb666cc3..81c52266ceefb4cd4ddfba02c9f09c0833f450ce 100644
--- a/base/process/process_metrics.h
+++ b/base/process/process_metrics.h
@@ -261,11 +261,13 @@ BASE_EXPORT void SetFdLimit(unsigned int max_descriptors);
 // Data about system-wide memory consumption. Values are in KB. Available on
 // Windows, Mac, Linux, Android and Chrome OS.
 //
-// Total/free memory are available on all platforms that implement
+// Total memory are available on all platforms that implement
 // GetSystemMemoryInfo(). Total/free swap memory are available on all platforms
 // except on Mac. Buffers/cached/active_anon/inactive_anon/active_file/
-// inactive_file/dirty/pswpin/pswpout/pgmajfault are available on
+// inactive_file/dirty/reclaimable/pswpin/pswpout/pgmajfault are available on
 // Linux/Android/Chrome OS. Shmem/slab/gem_objects/gem_size are Chrome OS only.
+// Speculative/file_backed/purgeable are Mac and iOS only.
+// Free is absent on Windows (see "avail_phys" below).
 struct BASE_EXPORT SystemMemoryInfoKB {
   SystemMemoryInfoKB();
   SystemMemoryInfoKB(const SystemMemoryInfoKB& other);
@@ -273,44 +275,64 @@ struct BASE_EXPORT SystemMemoryInfoKB {
   // Serializes the platform specific fields to value.
   std::unique_ptr<Value> ToValue() const;
 
-  int total;
-  int free;
+  int total = 0;
 
-#if defined(OS_LINUX)
+#if !defined(OS_WIN)
+  int free = 0;
+#endif
+
+#if defined(OS_WIN)
+  // "This is the amount of physical memory that can be immediately reused
+  // without having to write its contents to disk first. It is the sum of the
+  // size of the standby, free, and zero lists." (MSDN).
+  // Standby: not modified pages of physical ram (file-backed memory) that are
+  // not actively being used.
+  int avail_phys = 0;
+#endif
+
+#if defined(OS_LINUX) || defined(OS_ANDROID)
   // This provides an estimate of available memory as described here:
   // https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=34e431b0ae398fc54ea69ff85ec700722c9da773
   // NOTE: this is ONLY valid in kernels 3.14 and up.  Its value will always
   // be 0 in earlier kernel versions.
-  int available;
+  // Note: it includes _all_ file-backed memory (active + inactive).
+  int available = 0;
 #endif
 
 #if !defined(OS_MACOSX)
-  int swap_total;
-  int swap_free;
+  int swap_total = 0;
+  int swap_free = 0;
 #endif
 
 #if defined(OS_ANDROID) || defined(OS_LINUX)
-  int buffers;
-  int cached;
-  int active_anon;
-  int inactive_anon;
-  int active_file;
-  int inactive_file;
-  int dirty;
+  int buffers = 0;
+  int cached = 0;
+  int active_anon = 0;
+  int inactive_anon = 0;
+  int active_file = 0;
+  int inactive_file = 0;
+  int dirty = 0;
+  int reclaimable = 0;
 
   // vmstats data.
-  unsigned long pswpin;
-  unsigned long pswpout;
-  unsigned long pgmajfault;
+  unsigned long pswpin = 0;
+  unsigned long pswpout = 0;
+  unsigned long pgmajfault = 0;
 #endif  // defined(OS_ANDROID) || defined(OS_LINUX)
 
 #if defined(OS_CHROMEOS)
-  int shmem;
-  int slab;
+  int shmem = 0;
+  int slab = 0;
   // Gem data will be -1 if not supported.
-  int gem_objects;
-  long long gem_size;
+  int gem_objects = -1;
+  long long gem_size = -1;
 #endif  // defined(OS_CHROMEOS)
+
+#if defined(OS_MACOSX)
+  int speculative = 0;
+  int file_backed = 0;
+  int purgeable = 0;
+#endif  // defined(OS_MACOSX)
 };
 
 // On Linux/Android/Chrome OS, system-wide memory consumption data is parsed