workers: Move ownership of WebThread from WorkerThread

Source/core/workers/WorkerThreadStartupData.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 28 matching lines @@
     : m_scriptURL(scriptURL.copy())
     , m_userAgent(userAgent.isolatedCopy())
     , m_sourceCode(sourceCode.isolatedCopy())
     , m_cachedMetaData(cachedMetaData)
     , m_startMode(startMode)
     , m_contentSecurityPolicy(contentSecurityPolicy.isolatedCopy())
     , m_contentSecurityPolicyType(contentSecurityPolicyType)
     , m_starterOrigin(starterOrigin)
     , m_workerClients(workerClients)
     , m_v8CacheOptions(v8CacheOptions)
+    , m_thread(nullptr)
 {
 }
 
 WorkerThreadStartupData::~WorkerThreadStartupData()
 {
 }
 
 } // namespace blink