ServiceWorker::from can handle null ServiceWorkers

Source/modules/serviceworkers/ServiceWorker.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 122 matching lines @@
     case blink::WebServiceWorkerStateDeactivated:
         return deactivated;
     default:
         ASSERT_NOT_REACHED();
         return nullAtom;
     }
 }
 
 PassRefPtr<ServiceWorker> ServiceWorker::from(ExecutionContext* executionContext, WebType* worker)
 {
+    if (!worker)
+        return PassRefPtr<ServiceWorker>();
+
     blink::WebServiceWorkerProxy* proxy = worker->proxy();
     ServiceWorker* existingServiceWorker = proxy ? proxy->unwrap() : 0;
     if (existingServiceWorker) {
         ASSERT(existingServiceWorker->executionContext() == executionContext);
         return existingServiceWorker;
     }
 
     return create(executionContext, adoptPtr(worker));
 }
 
@@ skipping 32 matching lines @@
     , WebServiceWorkerProxy(this)
     , m_outerWorker(worker)
     , m_isPromisePending(false)
 {
     ScriptWrappable::init(this);
     ASSERT(m_outerWorker);
     m_outerWorker->setProxy(this);
 }
 
 } // namespace WebCore