mac: Fix calulation for number of resident pages in a process.

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..9a7fc290f0591e0c50d4e4554f89052d8809d3d9 100644
--- a/base/process/process_metrics.h
+++ b/base/process/process_metrics.h
@@ -136,8 +136,7 @@ class BASE_EXPORT ProcessMetrics {
   // memory currently allocated to a process that cannot be shared. Returns
   // false on platform specific error conditions.  Note: |private_bytes|
   // returns 0 on unsupported OSes: prior to XP SP2.
-  bool GetMemoryBytes(size_t* private_bytes,
-                      size_t* shared_bytes);
+  bool GetMemoryBytes(size_t* private_bytes, size_t* shared_bytes) const;
   // Fills a CommittedKBytes with both resident and paged
   // memory usage as per definition of CommittedBytes.
   void GetCommittedKBytes(CommittedKBytes* usage) const;