Add Notification.maxActions so websites know how many buttons we support

Source/modules/notifications/Notification.cpp

Index: Source/modules/notifications/Notification.cpp
diff --git a/Source/modules/notifications/Notification.cpp b/Source/modules/notifications/Notification.cpp
index 4ac301fe131c9af0bd40d396f9092e1d4da9c867..a6b1ca2576922a88ae369b9608557a0f178104e5 100644
--- a/Source/modules/notifications/Notification.cpp
+++ b/Source/modules/notifications/Notification.cpp
@@ -294,6 +294,11 @@ void Notification::requestPermission(ExecutionContext* context, NotificationPerm
         permissionClient->requestPermission(context, callback);
 }
 
+unsigned Notification::maxActions()
+{
+    return notificationManager()->maxActions();
+}
+
 bool Notification::dispatchEventInternal(PassRefPtrWillBeRawPtr<Event> event)
 {
     ASSERT(executionContext()->isContextThread());