Allow partial update for notification update API

chrome/browser/notifications/balloon_collection_impl.cc

Index: chrome/browser/notifications/balloon_collection_impl.cc
diff --git a/chrome/browser/notifications/balloon_collection_impl.cc b/chrome/browser/notifications/balloon_collection_impl.cc
index c7d0861331aca9d0e8c5eeb99742dcaa6220534a..3ee0c050748effffd822391776f1a12796e6fec0 100644
--- a/chrome/browser/notifications/balloon_collection_impl.cc
+++ b/chrome/browser/notifications/balloon_collection_impl.cc
@@ -92,8 +92,9 @@ void BalloonCollectionImpl::Add(const Notification& notification,
   AddImpl(notification, profile, false);
 }
 
-bool BalloonCollectionImpl::DoesIdExist(const std::string& id) {
-  return base_.DoesIdExist(id);
+const Notification* BalloonCollectionImpl::FindById(
+    const std::string& id) const {
+  return base_.FindById(id);
 }
 
 bool BalloonCollectionImpl::RemoveById(const std::string& id) {