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

chrome/browser/component_updater/pnacl/pnacl_updater_observer.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_COMPONENT_UPDATER_PNACL_PNACL_UPDATER_OBSERVER_H_
 #define CHROME_BROWSER_COMPONENT_UPDATER_PNACL_PNACL_UPDATER_OBSERVER_H_
 
 #include "base/compiler_specific.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 class PnaclComponentInstaller;
 
 // Monitors the component updater service, so that the callbacks registered
 // against the PnaclComponentInstaller can be notified of events.
 class PnaclUpdaterObserver : public content::NotificationObserver {
  public:
   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_;
   PnaclComponentInstaller* pnacl_installer_;
   DISALLOW_COPY_AND_ASSIGN(PnaclUpdaterObserver);
 };
 
 #endif  // CHROME_BROWSER_COMPONENT_UPDATER_PNACL_PNACL_UPDATER_OBSERVER_H_