Add experimental private memory footprint metrics.

chrome/browser/memory_details_mac.cc

Index: chrome/browser/memory_details_mac.cc
diff --git a/chrome/browser/memory_details_mac.cc b/chrome/browser/memory_details_mac.cc
index 571e739d694b780262f4b9db587a3641a48731b6..30d9e861c225d9ca02bdeece349e711dc9f1dffd 100644
--- a/chrome/browser/memory_details_mac.cc
+++ b/chrome/browser/memory_details_mac.cc
@@ -14,6 +14,7 @@
 #include "base/file_version_info.h"
 #include "base/files/file_path.h"
 #include "base/mac/foundation_util.h"
+#include "base/mac/mac_util.h"
 #include "base/process/process_iterator.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ -62,7 +63,16 @@ void CollectProcessDataForChromeProcess(
       base::ProcessMetrics::CreateProcessMetrics(
           pid, content::BrowserChildProcessHost::GetPortProvider());
   metrics->GetCommittedAndWorkingSetKBytes(&info.committed, &info.working_set);
-  info.phys_footprint = metrics->GetTaskVMInfo().phys_footprint;
+  base::ProcessMetrics::TaskVMInfo vm_info = metrics->GetTaskVMInfo();
+  info.phys_footprint = vm_info.phys_footprint;
+
+  // TODO(erikchen): Remove this temporary estimate for private memory once the
+  // memory infra service emits the same metric. https://crbug.com/720541.
+  if (base::mac::IsAtLeastOS10_12()) {
+    info.private_memory_footprint = vm_info.phys_footprint;

[Nico, 2017/05/11 20:12:59]

are you sure that you want to send differently computed things on different OS?
This means this metric will be useless to look at unless you split by os.

[erikchen, 2017/05/11 21:02:22]

Yup. The first API is strictly better, but not available on older OSes. This is
an experimental, temporary metric and I'll remember to split.

When we do this officially, we probably will want to have separately named UMA
metrics to avoid confusion.

+  } else {
+    info.private_memory_footprint = vm_info.internal + vm_info.compressed;
+  }
 
   processes->push_back(info);
 }