Shut down all threads before the main thread shuts down

third_party/WebKit/Source/platform/heap/ThreadState.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 414 matching lines @@
         m_orderedPreFinalizers.remove(PreFinalizer(self, &T::invokePreFinalizer));
     }
 
     void shouldFlushHeapDoesNotContainCache() { m_shouldFlushHeapDoesNotContainCache = true; }
 
     void registerTraceDOMWrappers(v8::Isolate* isolate, void (*traceDOMWrappers)(v8::Isolate*, Visitor*))
     {
         m_isolate = isolate;
         m_traceDOMWrappers = traceDOMWrappers;
     }
+    void unregisterTraceDOMWrappers()
+    {
+        m_isolate = nullptr;
+        m_traceDOMWrappers = nullptr;
+    }
 
     // By entering a gc-forbidden scope, conservative GCs will not
     // be allowed while handling an out-of-line allocation request.
     // Intended used when constructing subclasses of GC mixins, where
     // the object being constructed cannot be safely traced & marked
     // fully should a GC be allowed while its subclasses are being
     // constructed.
     void enterGCForbiddenScopeIfNeeded(GarbageCollectedMixinConstructorMarker* gcMixinMarker)
     {
         ASSERT(checkThread());
@@ skipping 262 matching lines @@
 
 template<> class ThreadStateFor<AnyThread> {
     STATIC_ONLY(ThreadStateFor);
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 } // namespace blink
 
 #endif // ThreadState_h