Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/safe_browsing/safe_browsing_service.h

Index: chrome/browser/safe_browsing/safe_browsing_service.h
diff --git a/chrome/browser/safe_browsing/safe_browsing_service.h b/chrome/browser/safe_browsing/safe_browsing_service.h
index b7d11234954210ce6f6d6c6de908db703f857c27..a756405108eaf70b320a3ab023dceaadaa5233de 100644
--- a/chrome/browser/safe_browsing/safe_browsing_service.h
+++ b/chrome/browser/safe_browsing/safe_browsing_service.h
@@ -20,6 +20,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
+#include "base/prefs/public/pref_observer.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "base/synchronization/lock.h"
 #include "base/time.h"
@@ -55,7 +56,8 @@ class DownloadProtectionService;
 class SafeBrowsingService
     : public base::RefCountedThreadSafe<
           SafeBrowsingService, content::BrowserThread::DeleteOnUIThread>,
-      public content::NotificationObserver {
+      public content::NotificationObserver,
+      public PrefObserver {
  public:
   class Client;
   // Users of this service implement this interface to be notified
@@ -486,6 +488,10 @@ class SafeBrowsingService
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
+  // PrefObserver override
+  virtual void OnPreferenceChanged(PrefServiceBase* service,
+                                   const std::string& pref_name) OVERRIDE;
+
   // Starts following the safe browsing preference on |pref_service|.
   void AddPrefService(PrefService* pref_service);