Introduce per-tab preferences service.

chrome/browser/prefs/pref_notifier_impl.h

Index: chrome/browser/prefs/pref_notifier_impl.h
diff --git a/chrome/browser/prefs/pref_notifier_impl.h b/chrome/browser/prefs/pref_notifier_impl.h
index b16ad1144fa02f0701cf2c5377c6fe4be433200a..edabf3f8fae4db74626016e7ce8362b1aede13b3 100644
--- a/chrome/browser/prefs/pref_notifier_impl.h
+++ b/chrome/browser/prefs/pref_notifier_impl.h
@@ -23,6 +23,7 @@ class NotificationObserver;
 class PrefNotifierImpl : public PrefNotifier,
                          public base::NonThreadSafe {
  public:
+  PrefNotifierImpl();
   explicit PrefNotifierImpl(PrefService* pref_service);
   virtual ~PrefNotifierImpl();
 
@@ -35,6 +36,8 @@ class PrefNotifierImpl : public PrefNotifier,
   virtual void OnPreferenceChanged(const std::string& pref_name);
   virtual void OnInitializationCompleted(bool succeeded);
 
+  void SetPrefService(PrefService* pref_service);
+
  protected:
   // A map from pref names to a list of observers. Observers get fired in the
   // order they are added. These should only be accessed externally for unit