Tidy up CompositorWorkerManager unit tests.

Source/core/workers/WorkerGlobalScope.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009, 2011 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 68 matching lines @@
     , m_eventQueue(WorkerEventQueue::create(this))
     , m_workerClients(workerClients)
     , m_timeOrigin(timeOrigin)
     , m_messageStorage(ConsoleMessageStorage::create())
     , m_workerExceptionUniqueIdentifier(0)
 {
     setSecurityOrigin(SecurityOrigin::create(url));
     if (starterOrigin)
         securityOrigin()->transferPrivilegesFrom(*starterOrigin);
 
-    m_workerClients->reattachThread();
+    if (m_workerClients)
+        m_workerClients->reattachThread();
+
     m_thread->setWorkerInspectorController(m_workerInspectorController.get());
 }
 
 WorkerGlobalScope::~WorkerGlobalScope()
 {
     ASSERT(!m_script);
     ASSERT(!m_workerInspectorController);
 }
 
 void WorkerGlobalScope::applyContentSecurityPolicyFromVector(const Vector<CSPHeaderAndType>& headers)
@@ skipping 294 matching lines @@
     visitor->trace(m_timers);
     visitor->trace(m_messageStorage);
     visitor->trace(m_pendingMessages);
     HeapSupplementable<WorkerGlobalScope>::trace(visitor);
 #endif
     ExecutionContext::trace(visitor);
     EventTargetWithInlineData::trace(visitor);
 }
 
 } // namespace blink