Experiment: disallow Persistent use by non-attached threads.

third_party/WebKit/Source/platform/heap/Persistent.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef Persistent_h
 #define Persistent_h
 
 #include "platform/heap/Member.h"
 #include "platform/heap/PersistentNode.h"
 #include "wtf/Allocator.h"
@@ skipping 162 matching lines @@
 
 private:
     NO_LAZY_SWEEP_SANITIZE_ADDRESS
     void assign(T* ptr)
     {
         if (crossThreadnessConfiguration == CrossThreadPersistentConfiguration)
             releaseStore(reinterpret_cast<void* volatile*>(&m_raw), ptr);
         else
             m_raw = ptr;
         checkPointer();
+        ASSERT(ThreadState::current());
         if (m_raw) {
             if (!m_persistentNode)
                 initialize();
             return;
         }
         uninitialize();
     }
 
     NO_LAZY_SWEEP_SANITIZE_ADDRESS
     void initialize()
@@ skipping 549 matching lines @@
     // into it.
     //
     // TODO(sof): remove this hack once wtf/Functional.h can also work with a type like
     // CrossThreadWeakPersistent<>.
     static WeakPtr<T> unwrap(const StorageType& value) { return WeakPtr<T>(WeakReference<T>::create(value.get())); }
 };
 
 } // namespace WTF
 
 #endif // Persistent_h