Add null checks in navigator.serviceWorker access to fix possible crash

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 52 matching lines @@
     }
 }
 
 ScriptPromise ServiceWorkerContainer::registerServiceWorker(ExecutionContext* executionContext, const String& url, const Dictionary& dictionary)
 {
     RegistrationOptionList options(dictionary);
     ASSERT(RuntimeEnabledFeatures::serviceWorkerEnabled());
     RefPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(executionContext);
     ScriptPromise promise = resolver->promise();
 
+    if (!m_provider) {
+        resolver->reject(DOMError::create(InvalidStateError, "No associated provider is available"));
+        return promise;
+    }
+
     RefPtr<SecurityOrigin> documentOrigin = executionContext->securityOrigin();
     KURL patternURL = executionContext->completeURL(options.scope);
     if (!documentOrigin->canRequest(patternURL)) {
         resolver->reject(DOMError::create(SecurityError, "Can only register for patterns in the document's origin."));
         return promise;
     }
 
     KURL scriptURL = executionContext->completeURL(url);
     if (!documentOrigin->canRequest(scriptURL)) {
         resolver->reject(DOMError::create(SecurityError, "Script must be in document's origin."));
         return promise;
     }
 
     m_provider->registerServiceWorker(patternURL, scriptURL, new CallbackPromiseAdapter<ServiceWorker, ServiceWorkerError>(resolver, executionContext));
     return promise;
 }
 
 ScriptPromise ServiceWorkerContainer::unregisterServiceWorker(ExecutionContext* executionContext, const String& pattern)
 {
     ASSERT(RuntimeEnabledFeatures::serviceWorkerEnabled());
     RefPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(executionContext);
     ScriptPromise promise = resolver->promise();
 
+    if (!m_provider) {
+        resolver->reject(DOMError::create(InvalidStateError, "No associated provider is available"));
+        return promise;
+    }
+
     RefPtr<SecurityOrigin> documentOrigin = executionContext->securityOrigin();
     KURL patternURL = executionContext->completeURL(pattern);
     if (!pattern.isEmpty() && !documentOrigin->canRequest(patternURL)) {
         resolver->reject(DOMError::create(SecurityError, "Can only unregister for patterns in the document's origin."));
-
         return promise;
     }
 
     m_provider->unregisterServiceWorker(patternURL, new CallbackPromiseAdapter<ServiceWorker, ServiceWorkerError>(resolver, executionContext));
     return promise;
 }
 
 ServiceWorkerContainer::ServiceWorkerContainer(ExecutionContext* executionContext)
-    : m_provider(ServiceWorkerContainerClient::from(executionContext)->provider())
+    : m_provider(0)
 {
     ScriptWrappable::init(this);
-    m_provider->setClient(this);
+
+    if (ServiceWorkerContainerClient* client = ServiceWorkerContainerClient::from(executionContext)) {
+        m_provider = client->provider();
+        if (m_provider)
+            m_provider->setClient(this);
+    }
 }
 
 } // namespace WebCore