Remove PrefObserver usage, batch 3.

base/prefs/public/pref_change_registrar.cc

Index: base/prefs/public/pref_change_registrar.cc
diff --git a/base/prefs/public/pref_change_registrar.cc b/base/prefs/public/pref_change_registrar.cc
index 0a442e729ce42aaf159dd5d7428807e297e62616..41b422d2ce5623c4e7a6c5f12fb0543951edc4be 100644
--- a/base/prefs/public/pref_change_registrar.cc
+++ b/base/prefs/public/pref_change_registrar.cc
@@ -91,3 +91,7 @@ void PrefChangeRegistrar::InvokeUnnamedCallback(const base::Closure& callback,
                                                 const std::string& pref_name) {
   callback.Run();
 }
+
+PrefServiceBase* PrefChangeRegistrar::prefs() {
+  return service_;
+}