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diff --git a/Source/JavaScriptCore/heap/WeakBlock.h b/Source/JavaScriptCore/heap/WeakBlock.h
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+++ b/Source/JavaScriptCore/heap/WeakBlock.h
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+/*
+ * Copyright (C) 2012 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
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef WeakBlock_h
+#define WeakBlock_h
+
+#include "HeapBlock.h"
+#include "WeakHandleOwner.h"
+#include "WeakImpl.h"
+#include <wtf/DoublyLinkedList.h>
+#include <wtf/PageAllocation.h>
+#include <wtf/StdLibExtras.h>
+
+namespace JSC {
+
+class HeapRootVisitor;
+class JSValue;
+class WeakHandleOwner;
+
+class WeakBlock : public DoublyLinkedListNode<WeakBlock> {
+public:
+    friend class WTF::DoublyLinkedListNode<WeakBlock>;
+    static const size_t blockSize = 4 * KB;
+
+    struct FreeCell {
+        FreeCell* next;
+    };
+
+    struct SweepResult {
+        SweepResult();
+        bool isNull() const;
+
+        bool blockIsFree;
+        FreeCell* freeList;
+    };
+
+    static WeakBlock* create();
+    static void destroy(WeakBlock*);
+
+    static WeakImpl* asWeakImpl(FreeCell*);
+
+    void sweep();
+    const SweepResult& sweepResult();
+    SweepResult takeSweepResult();
+
+    void visitLiveWeakImpls(HeapRootVisitor&);
+    void visitDeadWeakImpls(HeapRootVisitor&);
+
+    void finalizeAll();
+
+private:
+    static FreeCell* asFreeCell(WeakImpl*);
+
+    WeakBlock(PageAllocation&);
+    WeakImpl* firstWeakImpl();
+    void finalize(WeakImpl*);
+    WeakImpl* weakImpls();
+    size_t weakImplCount();
+    void addToFreeList(FreeCell**, WeakImpl*);
+
+    PageAllocation m_allocation;
+    WeakBlock* m_prev;
+    WeakBlock* m_next;
+    SweepResult m_sweepResult;
+};
+
+inline WeakBlock::SweepResult::SweepResult()
+    : blockIsFree(true)
+    , freeList(0)
+{
+    ASSERT(isNull());
+}
+
+inline bool WeakBlock::SweepResult::isNull() const
+{
+    return blockIsFree && !freeList; // This state is impossible, so we can use it to mean null.
+}
+
+inline WeakImpl* WeakBlock::asWeakImpl(FreeCell* freeCell)
+{
+    return reinterpret_cast<WeakImpl*>(freeCell);
+}
+
+inline WeakBlock::SweepResult WeakBlock::takeSweepResult()
+{
+    SweepResult tmp;
+    std::swap(tmp, m_sweepResult);
+    ASSERT(m_sweepResult.isNull());
+    return tmp;
+}
+
+inline const WeakBlock::SweepResult& WeakBlock::sweepResult()
+{
+    return m_sweepResult;
+}
+
+inline WeakBlock::FreeCell* WeakBlock::asFreeCell(WeakImpl* weakImpl)
+{
+    return reinterpret_cast<FreeCell*>(weakImpl);
+}
+
+inline void WeakBlock::finalize(WeakImpl* weakImpl)
+{
+    ASSERT(weakImpl->state() == WeakImpl::Dead);
+    weakImpl->setState(WeakImpl::Finalized);
+    WeakHandleOwner* weakHandleOwner = weakImpl->weakHandleOwner();
+    if (!weakHandleOwner)
+        return;
+    weakHandleOwner->finalize(Handle<Unknown>::wrapSlot(&const_cast<JSValue&>(weakImpl->jsValue())), weakImpl->context());
+}
+
+inline WeakImpl* WeakBlock::weakImpls()
+{
+    return reinterpret_cast<WeakImpl*>(this) + ((sizeof(WeakBlock) + sizeof(WeakImpl) - 1) / sizeof(WeakImpl));
+}
+
+inline size_t WeakBlock::weakImplCount()
+{
+    return (blockSize / sizeof(WeakImpl)) - ((sizeof(WeakBlock) + sizeof(WeakImpl) - 1) / sizeof(WeakImpl));
+}
+
+inline void WeakBlock::addToFreeList(FreeCell** freeList, WeakImpl* weakImpl)
+{
+    ASSERT(weakImpl->state() == WeakImpl::Deallocated);
+    FreeCell* freeCell = asFreeCell(weakImpl);
+    ASSERT(!*freeList || ((char*)*freeList > (char*)this && (char*)*freeList < (char*)this + blockSize));
+    ASSERT((char*)freeCell > (char*)this && (char*)freeCell < (char*)this + blockSize);
+    freeCell->next = *freeList;
+    *freeList = freeCell;
+}
+
+} // namespace JSC
+
+#endif // WeakBlock_h