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

base/process/process_metrics_linux.cc

Index: base/process/process_metrics_linux.cc
diff --git a/base/process/process_metrics_linux.cc b/base/process/process_metrics_linux.cc
index b14aa210bd57af5bd53c6581590fa221f355d9bb..5d542cc67527dad91035dcfc076e4f28b22ba25f 100644
--- a/base/process/process_metrics_linux.cc
+++ b/base/process/process_metrics_linux.cc
@@ -192,7 +192,7 @@ size_t ProcessMetrics::GetPeakWorkingSetSize() const {
 }
 
 bool ProcessMetrics::GetMemoryBytes(size_t* private_bytes,
-                                    size_t* shared_bytes) {
+                                    size_t* shared_bytes) const {
   WorkingSetKBytes ws_usage;
   if (!GetWorkingSetKBytes(&ws_usage))
     return false;