Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/protector/protected_prefs_watcher.cc

Index: chrome/browser/protector/protected_prefs_watcher.cc
diff --git a/chrome/browser/protector/protected_prefs_watcher.cc b/chrome/browser/protector/protected_prefs_watcher.cc
index b98438dce2f632d0dac760cf81d072b967bb79b5..ed13224ae40ae417f1299706a5ea1ee236ee8dd0 100644
--- a/chrome/browser/protector/protected_prefs_watcher.cc
+++ b/chrome/browser/protector/protected_prefs_watcher.cc
@@ -195,14 +195,10 @@ void ProtectedPrefsWatcher::ForceUpdateBackup() {
   InitBackup();
 }
 
-void ProtectedPrefsWatcher::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));
-  if (UpdateBackupEntry(*pref_name))
+void ProtectedPrefsWatcher::OnPreferenceChanged(PrefServiceBase* service,
+                                                const std::string& pref_name) {
+  DCHECK(pref_observer_.IsObserved(pref_name));
+  if (UpdateBackupEntry(pref_name))
     UpdateBackupSignature();
 }