Add ability to change default pref values, and use in BrowserInstantController.

base/prefs/pref_registry.cc

Index: base/prefs/pref_registry.cc
diff --git a/base/prefs/pref_registry.cc b/base/prefs/pref_registry.cc
index c6fad4eb33baef6979a01beb177f8f4831b84e76..6307bd44ea05663091ee063ad91f0700a3c024c0 100644
--- a/base/prefs/pref_registry.cc
+++ b/base/prefs/pref_registry.cc
@@ -16,18 +16,10 @@ PrefRegistry::PrefRegistry()
 PrefRegistry::~PrefRegistry() {
 }
 
-scoped_refptr<PrefStore> PrefRegistry::defaults() {
+scoped_refptr<DefaultPrefStore> PrefRegistry::defaults() {
   return defaults_.get();
 }
 
-PrefRegistry::const_iterator PrefRegistry::begin() const {
-  return defaults_->begin();
-}
-
-PrefRegistry::const_iterator PrefRegistry::end() const {
-  return defaults_->end();
-}
-
 void PrefRegistry::SetRegistrationCallback(
     const RegistrationCallback& callback) {
   registration_callback_ = callback;