Tidy up CompositorWorkerManager unit tests.

Source/core/workers/WorkerGlobalScope.cpp

Index: Source/core/workers/WorkerGlobalScope.cpp
diff --git a/Source/core/workers/WorkerGlobalScope.cpp b/Source/core/workers/WorkerGlobalScope.cpp
index d00edbe5b1efc7debd5a2d000b3d2110016b4478..6444e5b57eeb189894911f2001a0af9c762010fe 100644
--- a/Source/core/workers/WorkerGlobalScope.cpp
+++ b/Source/core/workers/WorkerGlobalScope.cpp
@@ -86,7 +86,9 @@ WorkerGlobalScope::WorkerGlobalScope(const KURL& url, const String& userAgent, W
     if (starterOrigin)
         securityOrigin()->transferPrivilegesFrom(*starterOrigin);
 
-    m_workerClients->reattachThread();
+    if (m_workerClients)
+        m_workerClients->reattachThread();
+
     m_thread->setWorkerInspectorController(m_workerInspectorController.get());
 }