Allow CrossThreadPersistent in collections

third_party/WebKit/Source/platform/heap/Heap.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 184 matching lines @@
     static inline bool isHeapObjectAlive(T* object)
     {
         static_assert(sizeof(T), "T must be fully defined");
         // The strongification of collections relies on the fact that once a
         // collection has been strongified, there is no way that it can contain
         // non-live entries, so no entries will be removed. Since you can't set
         // the mark bit on a null pointer, that means that null pointers are
         // always 'alive'.
         if (!object)
             return true;
+        // TODO(keishi): some tests create CrossThreadPersistent on non attached threads.
+        if (!ThreadState::current())

[sof, 2016/05/26 12:09:41]

What's going wrong without this bail out? I thought the predicate would just
inspect the mark bit in the header preceding |object|.

[keishi, 2016/05/26 12:32:04]

Sorry this is part of https://codereview.chromium.org/2012763002/ .
I used the wrong diff base.

I explain in the comments there, but the tests below seem to be creating
CrossThreadPersistents on non-oilpan attached threads.

+            return true;
         return ObjectAliveTrait<T>::isHeapObjectAlive(object);
     }
     template<typename T>
     static inline bool isHeapObjectAlive(const Member<T>& member)
     {
         return isHeapObjectAlive(member.get());
     }
     template<typename T>
     static inline bool isHeapObjectAlive(const WeakMember<T>& member)
     {
@@ skipping 379 matching lines @@
 void VisitorHelper<Derived>::handleWeakCell(Visitor* self, void* object)
 {
     T** cell = reinterpret_cast<T**>(object);
     if (*cell && !ObjectAliveTrait<T>::isHeapObjectAlive(*cell))
         *cell = nullptr;
 }
 
 } // namespace blink
 
 #endif // Heap_h