Disallow cross-thread Persistent<> read access.

third_party/WebKit/Source/core/workers/WorkerGlobalScope.h

 /*
  * Copyright (C) 2008, 2009 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 130 matching lines @@
   ScriptWrappable* getScriptWrappable() const final {
     return const_cast<WorkerGlobalScope*>(this);
   }
 
   double timeOrigin() const { return m_timeOrigin; }
   WorkerSettings* workerSettings() const { return m_workerSettings.get(); }
 
   WorkerOrWorkletScriptController* scriptController() final {
     return m_scriptController.get();
   }
-  WorkerClients* clients() { return m_workerClients.get(); }
+
+  WorkerClients* clients() const { return m_workerClients.get(); }
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
   WorkerGlobalScope(const KURL&,
                     const String& userAgent,
                     WorkerThread*,
                     double timeOrigin,
                     std::unique_ptr<SecurityOrigin::PrivilegeData>,
                     WorkerClients*);
@@ skipping 47 matching lines @@
 
 DEFINE_TYPE_CASTS(WorkerGlobalScope,
                   ExecutionContext,
                   context,
                   context->isWorkerGlobalScope(),
                   context.isWorkerGlobalScope());
 
 }  // namespace blink
 
 #endif  // WorkerGlobalScope_h