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diff --git a/Source/WebCore/dom/ComposedTreeAncestorIterator.h b/Source/WebCore/dom/ComposedTreeAncestorIterator.h
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+++ b/Source/WebCore/dom/ComposedTreeAncestorIterator.h
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+/*
+ * Copyright (C) 2015 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. ``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
+ * 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.
+ */
+
+#pragma once
+
+#include "HTMLSlotElement.h"
+#include "PseudoElement.h"
+#include "ShadowRoot.h"
+
+namespace WebCore {
+
+class HTMLSlotElement;
+
+class ComposedTreeAncestorIterator {
+public:
+    ComposedTreeAncestorIterator();
+    ComposedTreeAncestorIterator(Node& current);
+
+    Element& operator*() { return get(); }
+    Element* operator->() { return &get(); }
+
+    bool operator==(const ComposedTreeAncestorIterator& other) const { return m_current == other.m_current; }
+    bool operator!=(const ComposedTreeAncestorIterator& other) const { return m_current != other.m_current; }
+
+    ComposedTreeAncestorIterator& operator++() { return traverseParent(); }
+
+    Element& get() { return downcast<Element>(*m_current); }
+    ComposedTreeAncestorIterator& traverseParent();
+
+private:
+    void traverseParentInShadowTree();
+
+    Node* m_current { 0 };
+};
+
+inline ComposedTreeAncestorIterator::ComposedTreeAncestorIterator()
+{
+}
+
+inline ComposedTreeAncestorIterator::ComposedTreeAncestorIterator(Node& current)
+    : m_current(&current)
+{
+    ASSERT(!is<ShadowRoot>(m_current));
+}
+
+inline ComposedTreeAncestorIterator& ComposedTreeAncestorIterator::traverseParent()
+{
+    auto* parent = m_current->parentNode();
+    if (!parent) {
+        m_current = nullptr;
+        return *this;
+    }
+    if (is<ShadowRoot>(*parent)) {
+        m_current = downcast<ShadowRoot>(*parent).host();
+        return *this;
+    }
+    if (!is<Element>(*parent)) {
+        m_current = nullptr;
+        return *this;
+    };
+
+    if (auto* shadowRoot = parent->shadowRoot()) {
+        m_current = shadowRoot->findAssignedSlot(*m_current);
+        return *this;
+    }
+
+    m_current = parent;
+    return *this;
+}
+
+class ComposedTreeAncestorAdapter {
+public:
+    using iterator = ComposedTreeAncestorIterator;
+
+    ComposedTreeAncestorAdapter(Node& node)
+        : m_node(node)
+    { }
+
+    iterator begin()
+    {
+        if (is<ShadowRoot>(m_node))
+            return iterator(*downcast<ShadowRoot>(m_node).host());
+        if (is<PseudoElement>(m_node))
+            return iterator(*downcast<PseudoElement>(m_node).hostElement());
+        return iterator(m_node).traverseParent();
+    }
+    iterator end()
+    {
+        return iterator();
+    }
+    Element* first()
+    {
+        auto it = begin();
+        if (it == end())
+            return nullptr;
+        return &it.get();
+    }
+
+private:
+    Node& m_node;
+};
+
+// FIXME: We should have const versions too.
+inline ComposedTreeAncestorAdapter composedTreeAncestors(Node& node)
+{
+    return ComposedTreeAncestorAdapter(node);
+}
+
+} // namespace WebCore