Mac: Other approach for IPCing child task_ts.

chrome/browser/mach_broker_mac.h

Index: chrome/browser/mach_broker_mac.h
diff --git a/chrome/browser/mach_broker_mac.h b/chrome/browser/mach_broker_mac.h
index 67f4fec48712c9529d84980eb2ad48f45a73e37b..1827fc930c18d8eaa78fedb161770ba933ef6815 100644
--- a/chrome/browser/mach_broker_mac.h
+++ b/chrome/browser/mach_broker_mac.h
@@ -13,6 +13,7 @@
 #include "base/process.h"
 #include "base/process_util.h"
 #include "base/singleton.h"
+#include "chrome/common/notification_registrar.h"
 
 // On OS X, the mach_port_t of a process is required to collect metrics about
 // the process. Running |task_for_pid()| is only allowed for privileged code.
@@ -28,7 +29,8 @@
 //
 // Since this data arrives over a separate channel, it is not available
 // immediately after a child process has been started.
-class MachBroker : public base::ProcessMetrics::PortProvider {
+class MachBroker : public base::ProcessMetrics::PortProvider,
+                   public NotificationObserver {
  public:
   // Returns the global MachBroker.
   static MachBroker* instance();
@@ -53,9 +55,18 @@ class MachBroker : public base::ProcessMetrics::PortProvider {
   // Implement |ProcessMetrics::PortProvider|.
   virtual mach_port_t TaskForPid(base::ProcessHandle process) const;
 
+  // Implement |NotificationObserver|.
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
  private:
   // Private constructor.
-  MachBroker() {}
+  MachBroker();
+  
+  // Used to register for notifications received by NotificationObserver.
+  // Accessed only on the UI thread.
+  NotificationRegistrar registrar_;
+  
   friend struct DefaultSingletonTraits<MachBroker>;
   friend class MachBrokerTest;
 
@@ -66,6 +77,7 @@ class MachBroker : public base::ProcessMetrics::PortProvider {
   // Mutex that guards |mach_map_|.
   mutable Lock lock_;
 
+  friend class RegisterNotificationTask;
   DISALLOW_COPY_AND_ASSIGN(MachBroker);
 };