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..92352ff37c03abd087f2318947e679b03cbc4033 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 +277,23 @@ struct BASE_EXPORT SystemMemoryInfoKB {
   int total;
   int free;
 
-#if defined(OS_LINUX)
+#if defined(OS_WIN)
+  // There are Free and Zero memory on Windows platform.
+  // See "Memory Management" and "Memory Performance Information"
+  // articles at MSDN.
+  int zero;

[Primiano Tucci (use gerrit), 2017/02/20 14:13:27]

Why this needs to be exposed at an API level? I understand if you need this to
do some calculation, but I am not sure we want to expose this detail through the
public-facing API.

[Michael K. (Yandex Team), 2017/02/20 14:33:13]

You're right: currently nobody uses it.
...Except process_metrics_unittest: "zero" memory is very similar to "free" on
Windows. And sometimes "free" can be null ( == 0) and zero can be null, but zero
+ free > 0.
Maybe in a future somebody will want "zero" memory.
(My thoughts: "free" is useless on Win without zero).

Ok, I can remove it.

+
+  // "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.
+  // Note: on Windows this field has a bit different meaning from the Linux one.
+  // On Linux "available" includes _all_ file-backed memory (active + inactive).

[Primiano Tucci (use gerrit), 2017/02/20 14:13:27]

note that you are saying "on linux" but this line is really about windows only
(look at the #ifdef)

[Michael K. (Yandex Team), 2017/02/20 14:33:14]

Because I wanted to explain what "different" exactly means.

Ok, I'll put that sentence in the linux section.

+  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 +314,7 @@ struct BASE_EXPORT SystemMemoryInfoKB {
   int active_file;
   int inactive_file;
   int dirty;
+  int reclaimable;
 
   // vmstats data.
   unsigned long pswpin;
@@ -311,6 +329,12 @@ 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