[Mac] Add a perf test that counts the number of Mach ports in the browser.

base/mach_ipc_mac.h

Index: base/mach_ipc_mac.h
diff --git a/base/mach_ipc_mac.h b/base/mach_ipc_mac.h
index 7d39101965e735f691f188756d4848e955cb4772..9c2698e6f93f675dfa1f1875cc0118d31e0138fc 100644
--- a/base/mach_ipc_mac.h
+++ b/base/mach_ipc_mac.h
@@ -309,6 +309,19 @@ class BASE_EXPORT MachPortSender {
   DISALLOW_COPY_AND_ASSIGN(MachPortSender);
 };
 
+//==============================================================================
+// Static utility functions.
+
+namespace mac {
+
+// Returns the number of Mach ports to which the given task has a right.
+// Note that unless the calling task has send rights to the passed task port,
+// this will fail unless the calling task is running as root.
+kern_return_t BASE_EXPORT GetNumberOfMachPorts(mach_port_t task_port,
+                                               int* port_count);
+
+}  // namespace mac
+
 }  // namespace base
 
 #endif // BASE_MACH_IPC_MAC_H_