Use toDocument instead of static_cast<Document*>.

Source/core/workers/WorkerMessagingProxy.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 245 matching lines @@
 {
     ASSERT(!m_workerObject);
     ASSERT((m_scriptExecutionContext->isDocument() && isMainThread())
            || (m_scriptExecutionContext->isWorkerGlobalScope() && static_cast<WorkerGlobalScope*>(m_scriptExecutionContext.get())->thread()->isCurrentThread()));
 }
 
 void WorkerMessagingProxy::startWorkerGlobalScope(const KURL& scriptURL, const String& userAgent, const String& sourceCode, WorkerThreadStartMode startMode)
 {
     // FIXME: This need to be revisited when we support nested worker one day
     ASSERT(m_scriptExecutionContext->isDocument());
-    Document* document = static_cast<Document*>(m_scriptExecutionContext.get());
+    Document* document = toDocument(m_scriptExecutionContext.get());
     RefPtr<DedicatedWorkerThread> thread = DedicatedWorkerThread::create(scriptURL, userAgent, sourceCode, *this, *this, startMode, document->contentSecurityPolicy()->deprecatedHeader(), document->contentSecurityPolicy()->deprecatedHeaderType(), document->topOrigin(), document->loader()->timing()->referenceMonotonicTime());
     workerThreadCreated(thread);
     thread->start();
     InspectorInstrumentation::didStartWorkerGlobalScope(m_scriptExecutionContext.get(), this, scriptURL);
 }
 
 void WorkerMessagingProxy::postMessageToWorkerObject(PassRefPtr<SerializedScriptValue> message, PassOwnPtr<MessagePortChannelArray> channels)
 {
     m_scriptExecutionContext->postTask(MessageWorkerTask::create(message, channels, this));
 }
@@ skipping 189 matching lines @@
 
     m_workerThreadHadPendingActivity = hasPendingActivity;
 }
 
 bool WorkerMessagingProxy::hasPendingActivity() const
 {
     return (m_unconfirmedMessageCount || m_workerThreadHadPendingActivity) && !m_askedToTerminate;
 }
 
 } // namespace WebCore