ServiceWorker: Introduce ExtendableMessageEvent to replace MessageEvent

Source/modules/serviceworkers/ServiceWorkerRegistration.cpp

Index: Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
diff --git a/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp b/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
index cf94bd521093010a71a84420d370e05d490051f3..7e6a3cad8351e7462e0a72ebd6684f8a4b3467bf 100644
--- a/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
+++ b/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
@@ -97,6 +97,7 @@ void ServiceWorkerRegistration::update(ScriptState* scriptState, ExceptionState&
 
 ScriptPromise ServiceWorkerRegistration::unregister(ScriptState* scriptState)
 {
+
     RefPtrWillBeRawPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = resolver->promise();
 
@@ -164,6 +165,7 @@ void ServiceWorkerRegistration::stop()
     if (m_stopped)
         return;
     m_stopped = true;
+    m_provider = 0;
     m_outerRegistration->proxyStopped();
 }