Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/protector/base_prefs_change.cc

Index: chrome/browser/protector/base_prefs_change.cc
diff --git a/chrome/browser/protector/base_prefs_change.cc b/chrome/browser/protector/base_prefs_change.cc
index 2a4a8719ef7e8ac899bd85562c2f1f4b2458a155..9ca25c8930524bbb2ad595426ef8bd264132107b 100644
--- a/chrome/browser/protector/base_prefs_change.cc
+++ b/chrome/browser/protector/base_prefs_change.cc
@@ -43,12 +43,9 @@ void BasePrefsChange::IgnorePrefChanges() {
   pref_observer_.RemoveAll();
 }
 
-void BasePrefsChange::Observe(int type,
-                             const content::NotificationSource& source,
-                             const content::NotificationDetails& details) {
-  DCHECK(type == chrome::NOTIFICATION_PREF_CHANGED);
-  const std::string* pref_name = content::Details<std::string>(details).ptr();
-  DCHECK(pref_name && pref_observer_.IsObserved(*pref_name));
+void BasePrefsChange::OnPreferenceChanged(PrefServiceBase* service,
+                                          const std::string& pref_name) {
+  DCHECK(pref_observer_.IsObserved(pref_name));
   // Will delete this instance.
   ProtectorServiceFactory::GetForProfile(profile())->DismissChange(this);
 }