Allow partial update for notification update API

chrome/browser/notifications/balloon_collection_base.cc

Index: chrome/browser/notifications/balloon_collection_base.cc
diff --git a/chrome/browser/notifications/balloon_collection_base.cc b/chrome/browser/notifications/balloon_collection_base.cc
index c7487390bb5dc8cecbe70e52268bc58d9c05cebe..b69673e8f70aab629a686278cc3966713155a0a6 100644
--- a/chrome/browser/notifications/balloon_collection_base.cc
+++ b/chrome/browser/notifications/balloon_collection_base.cc
@@ -35,11 +35,15 @@ void BalloonCollectionBase::Remove(Balloon* balloon) {
   }
 }
 
-bool BalloonCollectionBase::DoesIdExist(const std::string& id) {
+bool BalloonCollectionBase::DoesIdExist(const std::string& id,
+                                        Notification* matched_notification) {
   Balloons::iterator iter;
   for (iter = balloons_.begin(); iter != balloons_.end(); ++iter) {
-    if ((*iter)->notification().notification_id() == id)
+    if ((*iter)->notification().notification_id() == id) {
+      if (matched_notification)
+        *matched_notification = (*iter)->notification();
       return true;
+    }
   }
   return false;
 }