Consistently use notifications from component updater w/ on-demand PNaCl.

chrome/browser/component_updater/pnacl/pnacl_updater_observer.h

Index: chrome/browser/component_updater/pnacl/pnacl_updater_observer.h
diff --git a/chrome/browser/component_updater/pnacl/pnacl_updater_observer.h b/chrome/browser/component_updater/pnacl/pnacl_updater_observer.h
index 48a6f0d9c81cbceb527da5478be4d0220ec1638f..598aa443d1668b59e909147f07efa1019790c501 100644
--- a/chrome/browser/component_updater/pnacl/pnacl_updater_observer.h
+++ b/chrome/browser/component_updater/pnacl/pnacl_updater_observer.h
@@ -18,10 +18,15 @@ class PnaclUpdaterObserver : public content::NotificationObserver {
   explicit PnaclUpdaterObserver(PnaclComponentInstaller* installer);
   virtual ~PnaclUpdaterObserver();
 
-  virtual void Observe(
-      int type,
-      const content::NotificationSource& source,
-      const content::NotificationDetails& details) OVERRIDE;
+  // Make sure that this has registered to observe relevant notifications.
+  void EnsureObserving();
+
+  // Unregister for observing notifcations.
+  void StopObserving();
+
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
 
  private:
   content::NotificationRegistrar registrar_;