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

Source/modules/notifications/Notification.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 85 matching lines @@
 
     TextDirection direction() const;
     KURL iconURL() const { return m_iconUrl; }
     SerializedScriptValue* serializedData() const { return m_serializedData.get(); }
 
     static String permissionString(WebNotificationPermission);
     static String permission(ExecutionContext*);
     static WebNotificationPermission checkPermission(ExecutionContext*);
     static void requestPermission(ExecutionContext*, NotificationPermissionCallback* = nullptr);
 
+    static unsigned maxActions();
+
     // EventTarget interface.
     ExecutionContext* executionContext() const final { return ActiveDOMObject::executionContext(); }
     const AtomicString& interfaceName() const override;
 
     // ActiveDOMObject interface.
     void stop() override;
     bool hasPendingActivity() const override;
 
     DECLARE_VIRTUAL_TRACE();
 
@@ skipping 53 matching lines @@
     void setState(NotificationState state) { m_state = state; }
 
     NotificationState m_state;
 
     AsyncMethodRunner<Notification> m_asyncRunner;
 };
 
 } // namespace blink
 
 #endif // Notification_h