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

base/process/process_metrics_openbsd.cc

Index: base/process/process_metrics_openbsd.cc
diff --git a/base/process/process_metrics_openbsd.cc b/base/process/process_metrics_openbsd.cc
index 58033aef62e75110d27978a75e21fbe2f7affbdb..d8fbe7e3710ab7a7cecbc6643d72cb434e119b61 100644
--- a/base/process/process_metrics_openbsd.cc
+++ b/base/process/process_metrics_openbsd.cc
@@ -64,7 +64,7 @@ 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))