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

base/process/process_metrics_freebsd.cc

Index: base/process/process_metrics_freebsd.cc
diff --git a/base/process/process_metrics_freebsd.cc b/base/process/process_metrics_freebsd.cc
index 686f6338724da2e11a08ff3c5c4231b833029ccd..4f5adf790f68276b94c87935cdb7c5c032ac438e 100644
--- a/base/process/process_metrics_freebsd.cc
+++ b/base/process/process_metrics_freebsd.cc
@@ -58,7 +58,7 @@ 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;