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

public/platform/modules/notifications/WebNotificationManager.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebNotificationManager_h
 #define WebNotificationManager_h
 
 #include "public/platform/WebCallbacks.h"
 #include "public/platform/WebString.h"
 #include "public/platform/WebVector.h"
@@ skipping 40 matching lines @@
 
     // Closes a persistent notification identified by its persistent notification Id.
     virtual void closePersistent(const WebSecurityOrigin&, int64_t persistentNotificationId) = 0;
 
     // Indicates that the delegate object is being destroyed, and must no longer
     // be used by the embedder to dispatch events.
     virtual void notifyDelegateDestroyed(WebNotificationDelegate*) = 0;
 
     // Synchronously checks the permission level for the given origin.
     virtual WebNotificationPermission checkPermission(const WebSecurityOrigin&) = 0;
+
+    // Returns the maximum number of actions supported by the embedder.
+    // TODO(johnme): Make pure virtual.
+    virtual size_t maxActions() { return 0; }
 };
 
 } // namespace blink
 
 #endif // WebNotificationManager_h