Add the UMA metric Memory.Gpu.PhysicalFootprint.MacOS

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 1562e7b156af082292b3c8a4753a4b26fb7ecfcd..2652bef85e519bb7d4bb6296846db6c4b7e8cbfe 100644
--- a/base/process/process_metrics.h
+++ b/base/process/process_metrics.h
@@ -162,6 +162,12 @@ class BASE_EXPORT ProcessMetrics {
   // system call.
   bool GetCommittedAndWorkingSetKBytes(CommittedKBytes* usage,
                                        WorkingSetKBytes* ws_usage) const;
+
+  // Returns the physical footprint, only available on macOS 10.11+. This
+  // measures anonymous, non-discardable memory. Returns 0 on error, or if the
+  // measurement was unavailable.
+  size_t GetPhysicalFootprint() const;
+
   // Returns private, shared, and total resident bytes. |locked_bytes| refers to
   // bytes that must stay resident. |locked_bytes| only counts bytes locked by
   // this task, not bytes locked by the kernel.