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..a9cadc8ffeebbd64d49579afe0fd8dfc3a900f60 100644
--- a/base/process/process_metrics.h
+++ b/base/process/process_metrics.h
@@ -264,8 +264,9 @@ BASE_EXPORT void SetFdLimit(unsigned int max_descriptors);
 // Total/free 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.
 struct BASE_EXPORT SystemMemoryInfoKB {
   SystemMemoryInfoKB();
   SystemMemoryInfoKB(const SystemMemoryInfoKB& other);
@@ -276,7 +277,13 @@ struct BASE_EXPORT SystemMemoryInfoKB {
   int total;
   int free;
 
-#if defined(OS_LINUX)
+#if defined(OS_WIN)
+  int zero;

[Primiano Tucci (use gerrit), 2017/02/15 11:18:33]

what is this?

[Michael K. (Yandex Team), 2017/02/17 13:38:47]

Done.

+  // On Windows this field has different meaning from the Linux one.

[Primiano Tucci (use gerrit), 2017/02/15 11:18:33]

nit: add a newline.
Also would be nice to explain what the meaning is, instead of saying "it's
different"

[Michael K. (Yandex Team), 2017/02/17 13:38:48]

Done.

+  int available;
+#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
@@ -297,6 +304,7 @@ struct BASE_EXPORT SystemMemoryInfoKB {
   int active_file;
   int inactive_file;
   int dirty;
+  int reclaimable;
 
   // vmstats data.
   unsigned long pswpin;
@@ -311,6 +319,12 @@ struct BASE_EXPORT SystemMemoryInfoKB {
   int gem_objects;
   long long gem_size;
 #endif  // defined(OS_CHROMEOS)
+
+#if defined(OS_MACOSX) || defined(OS_IOS)
+  int speculative;
+  int file_backed;
+  int purgeable;
+#endif
 };
 
 // On Linux/Android/Chrome OS, system-wide memory consumption data is parsed