Add NotificationOptions.actions so websites can provide buttons (blink)

Source/modules/notifications/Notification.idl

Index: Source/modules/notifications/Notification.idl
diff --git a/Source/modules/notifications/Notification.idl b/Source/modules/notifications/Notification.idl
index 80dc01ffffa5b1efc4da310e9a131dca64f2f940..76823c7173e9b8d6280331c4b40c6b22528c15e0 100644
--- a/Source/modules/notifications/Notification.idl
+++ b/Source/modules/notifications/Notification.idl
@@ -72,5 +72,8 @@ enum NotificationPermission {
     readonly attribute boolean silent;
     [CallWith=ScriptState] readonly attribute any data;
 
+    // TODO(johnme): The spec requires a FrozenArray, but sequence seems to behave like one already?! https://crbug.com/515920
+    [RuntimeEnabled=NotificationExperimental] readonly attribute sequence<NotificationAction> actions;
+
     [MeasureAs=NotificationClosed] void close();
 };