Introduce per-tab preferences service.

chrome/browser/prefs/pref_notifier_impl.cc

Index: chrome/browser/prefs/pref_notifier_impl.cc
diff --git a/chrome/browser/prefs/pref_notifier_impl.cc b/chrome/browser/prefs/pref_notifier_impl.cc
index ec5352bcae54d5b63881271e6887991feafb589e..3c23879ee06677892856a6f8c514f5fb9e665444 100644
--- a/chrome/browser/prefs/pref_notifier_impl.cc
+++ b/chrome/browser/prefs/pref_notifier_impl.cc
@@ -10,6 +10,10 @@
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_service.h"
 
+PrefNotifierImpl::PrefNotifierImpl()
+    : pref_service_(NULL) {
+}
+
 PrefNotifierImpl::PrefNotifierImpl(PrefService* service)
     : pref_service_(service) {
 }
@@ -104,3 +108,8 @@ void PrefNotifierImpl::FireObservers(const std::string& path) {
                       content::Details<const std::string>(&path));
   }
 }
+
+void PrefNotifierImpl::SetPrefService(PrefService* pref_service) {
+  DCHECK(pref_service_ == NULL);
+  pref_service_ = pref_service;
+}