The "push" event should inherit from ExtendableEvent.

Source/modules/push_messaging/PushEvent.cpp

Index: Source/modules/push_messaging/PushEvent.cpp
diff --git a/Source/modules/push_messaging/PushEvent.cpp b/Source/modules/push_messaging/PushEvent.cpp
index 37fe117398816f68e4a3303196d76bd5f899fa7a..07ae8f27a1e14792e4b6f37c157ca11965059a8b 100644
--- a/Source/modules/push_messaging/PushEvent.cpp
+++ b/Source/modules/push_messaging/PushEvent.cpp
@@ -15,14 +15,14 @@ PushEvent::PushEvent()
 {
 }
 
-PushEvent::PushEvent(const AtomicString& type, const String& data)
-    : Event(type, /*canBubble=*/false, /*cancelable=*/false)
+PushEvent::PushEvent(const AtomicString& type, const String& data, WaitUntilObserver* observer)
+    : ExtendableEvent(type, ExtendableEventInit(), observer)
     , m_data(data)
 {
 }
 
 PushEvent::PushEvent(const AtomicString& type, const PushEventInit& initializer)
-    : Event(type, initializer)
+    : ExtendableEvent(type, initializer)
     , m_data(initializer.data)
 {
 }