Don't leak a WebServiceWorker when 'current' races with context destruction.

Source/modules/serviceworkers/ServiceWorkerContainer.cpp

 /*
  * 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 124 matching lines @@
         resolver->reject(DOMException::create(SecurityError, "Can only unregister for patterns in the document's origin."));
         return promise;
     }
 
     m_provider->unregisterServiceWorker(patternURL, new CallbackPromiseAdapter<UndefinedValue, ServiceWorkerError>(resolver));
     return promise;
 }
 
 void ServiceWorkerContainer::setCurrentServiceWorker(blink::WebServiceWorker* serviceWorker)
 {
-    if (!executionContext())
+    if (!executionContext()) {
+        delete serviceWorker;
         return;
+    }
     m_current = ServiceWorker::create(executionContext(), adoptPtr(serviceWorker));
 }
 
 void ServiceWorkerContainer::dispatchMessageEvent(const blink::WebString& message, const blink::WebMessagePortChannelArray& webChannels)
 {
     if (!executionContext() || !window())
         return;
 
     OwnPtr<MessagePortArray> ports = MessagePort::toMessagePortArray(executionContext(), webChannels);
     RefPtr<SerializedScriptValue> value = SerializedScriptValue::createFromWire(message);
@@ skipping 11 matching lines @@
         return;
 
     if (ServiceWorkerContainerClient* client = ServiceWorkerContainerClient::from(executionContext)) {
         m_provider = client->provider();
         if (m_provider)
             m_provider->setClient(this);
     }
 }
 
 } // namespace WebCore