Remove content::NotificationObserver dependency from most Prefs code.

chrome/browser/prefs/pref_service.cc

Index: chrome/browser/prefs/pref_service.cc
diff --git a/chrome/browser/prefs/pref_service.cc b/chrome/browser/prefs/pref_service.cc
index eedef9bb3dd9c78ae5832f513b057feb0e252687..4839a1cd685e71ebcfcb2aef9c4df6b0c21bb4af 100644
--- a/chrome/browser/prefs/pref_service.cc
+++ b/chrome/browser/prefs/pref_service.cc
@@ -769,16 +769,18 @@ const ListValue* PrefService::GetList(const char* path) const {
   return static_cast<const ListValue*>(value);
 }
 
-void PrefService::AddPrefObserver(const char* path,
-                                  content::NotificationObserver* obs) {
+void PrefService::AddPrefObserver(const char* path, PrefObserver* obs) {
   pref_notifier_->AddPrefObserver(path, obs);
 }
 
-void PrefService::RemovePrefObserver(const char* path,
-                                     content::NotificationObserver* obs) {
+void PrefService::RemovePrefObserver(const char* path, PrefObserver* obs) {
   pref_notifier_->RemovePrefObserver(path, obs);
 }
 
+void PrefService::AddPrefInitObserver(base::Callback<void(bool)> obs) {
+  pref_notifier_->AddInitObserver(obs);
+}
+
 void PrefService::RegisterPreference(const char* path,
                                      Value* default_value,
                                      PrefSyncStatus sync_status) {