Tidy up CompositorWorkerManager unit tests.

Source/core/workers/WorkerThreadStartupData.h

 /*
  * 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 66 matching lines @@
     // See SecurityOrigin::transferPrivilegesFrom() for details on what
     // privileges are transferred.
     const SecurityOrigin* m_starterOrigin;
 
     // This object is created and initialized on the thread creating
     // a new worker context, but ownership of it and this WorkerThreadStartupData
     // structure is passed along to the new worker thread, where it is finalized.
     //
     // Hence, CrossThreadPersistent<> is required to allow finalization
     // to happen on a thread different than the thread creating the
-    // persistent reference.
+    // persistent reference. If the worker thread creation context
+    // supplies no extra 'clients', m_workerClients can be left as empty/null.
     OwnPtrWillBeCrossThreadPersistent<WorkerClients> m_workerClients;
 
     V8CacheOptions m_v8CacheOptions;
 
 private:
     WorkerThreadStartupData(const KURL& scriptURL, const String& userAgent, const String& sourceCode, PassOwnPtr<Vector<char>> cachedMetaData, WorkerThreadStartMode, const PassOwnPtr<Vector<CSPHeaderAndType>> contentSecurityPolicyHeaders, const SecurityOrigin*, PassOwnPtrWillBeRawPtr<WorkerClients>, V8CacheOptions);
 };
 
 } // namespace blink
 
 #endif // WorkerThreadStartupData_h