Mac: Create a pid->task_t mapping in the browser process.

base/process_util.h

Index: base/process_util.h
diff --git a/base/process_util.h b/base/process_util.h
index 2bb53964cfc1d759559608f7c203d011d54d4268..cec37bdfcaef3a84c997c0cc1e94f9823168bd90 100644
--- a/base/process_util.h
+++ b/base/process_util.h
@@ -369,9 +369,10 @@ class ProcessMetrics {
 #else
   class PortProvider {
    public:
-    // Should return the mach task for |process| if possible, or else 0. Only
-    // processes that this returns tasks for will have metrics on OS X (except
-    // for the current process, which always gets metrics).
+    // Should return the mach task for |process| if possible, or else
+    // |MACH_PORT_NULL|. Only processes that this returns tasks for will have
+    // metrics on OS X (except for the current process, which always gets
+    // metrics).
     virtual mach_port_t TaskForPid(ProcessHandle process) const = 0;
   };