The "push" event should inherit from ExtendableEvent.

Source/modules/serviceworkers/WaitUntilObserver.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 WaitUntilObserver_h
 #define WaitUntilObserver_h
 
 #include "core/dom/ContextLifecycleObserver.h"
 #include "modules/serviceworkers/ServiceWorkerGlobalScopeClient.h"
 #include "wtf/Forward.h"
 #include "wtf/RefCounted.h"
 
 namespace blink {
 
 class ExecutionContext;
 class ScriptState;
 class ScriptValue;
 
 // Created for each ExtendableEvent instance.
 class WaitUntilObserver final : public GarbageCollectedFinalized<WaitUntilObserver>, public ContextLifecycleObserver {
 public:
     enum EventType {
         Activate,
         Install,
         NotificationClick,
-        NotificationError
+        NotificationError,
+        Push
     };
 
     static WaitUntilObserver* create(ExecutionContext*, EventType, int eventID);
 
     // Must be called before and after dispatching the event.
     void willDispatchEvent();
     void didDispatchEvent(bool errorOccurred);
 
     // Observes the promise and delays calling the continuation until
     // the given promise is resolved or rejected.
@@ skipping 13 matching lines @@
 
     EventType m_type;
     int m_eventID;
     int m_pendingActivity;
     bool m_hasError;
 };
 
 } // namespace blink
 
 #endif // WaitUntilObserver_h