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diff --git a/Source/WebCore/html/CollectionTraversal.h b/Source/WebCore/html/CollectionTraversal.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. 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.
+ */
+
+#pragma once
+
+#include "CollectionType.h"
+#include "ElementChildIterator.h"
+#include "ElementDescendantIterator.h"
+
+namespace WebCore {
+
+template <CollectionTraversalType traversalType>
+struct CollectionTraversal { };
+
+template <>
+struct CollectionTraversal<CollectionTraversalType::Descendants> {
+    using Iterator = ElementDescendantIterator;
+
+    static ElementDescendantIterator end(ContainerNode&) { return ElementDescendantIterator(); }
+
+    template <typename CollectionClass>
+    static ElementDescendantIterator begin(const CollectionClass&, ContainerNode& rootNode);
+
+    template <typename CollectionClass>
+    static ElementDescendantIterator last(const CollectionClass&, ContainerNode& rootNode);
+
+    template <typename CollectionClass>
+    static void traverseForward(const CollectionClass&, ElementDescendantIterator& current, unsigned count, unsigned& traversedCount);
+
+    template <typename CollectionClass>
+    static void traverseBackward(const CollectionClass&, ElementDescendantIterator& current, unsigned count);
+};
+
+template <typename CollectionClass>
+inline ElementDescendantIterator CollectionTraversal<CollectionTraversalType::Descendants>::begin(const CollectionClass& collection, ContainerNode& rootNode)
+{
+    auto descendants = elementDescendants(rootNode);
+    auto end = descendants.end();
+    for (auto it = descendants.begin(); it != end; ++it) {
+        if (collection.elementMatches(*it)) {
+            // Drop iterator assertions because HTMLCollections / NodeList use a fine-grained invalidation scheme.
+            it.dropAssertions();
+            return it;
+        }
+    }
+    return end;
+}
+
+template <typename CollectionClass>
+inline ElementDescendantIterator CollectionTraversal<CollectionTraversalType::Descendants>::last(const CollectionClass& collection, ContainerNode& rootNode)
+{
+    auto descendants = elementDescendants(rootNode);
+    ElementDescendantIterator invalid;
+    for (auto it = descendants.last(); it != invalid; --it) {
+        if (collection.elementMatches(*it)) {
+            // Drop iterator assertions because HTMLCollections / NodeList use a fine-grained invalidation scheme.
+            it.dropAssertions();
+            return it;
+        }
+    }
+    return invalid;
+}
+
+template <typename CollectionClass>
+inline void CollectionTraversal<CollectionTraversalType::Descendants>::traverseForward(const CollectionClass& collection, ElementDescendantIterator& current, unsigned count, unsigned& traversedCount)
+{
+    ASSERT(collection.elementMatches(*current));
+    ElementDescendantIterator invalid;
+    for (traversedCount = 0; traversedCount < count; ++traversedCount) {
+        do {
+            ++current;
+            if (current == invalid)
+                return;
+        } while (!collection.elementMatches(*current));
+    }
+}
+
+template <typename CollectionClass>
+inline void CollectionTraversal<CollectionTraversalType::Descendants>::traverseBackward(const CollectionClass& collection, ElementDescendantIterator& current, unsigned count)
+{
+    ASSERT(collection.elementMatches(*current));
+    ElementDescendantIterator invalid;
+    for (; count; --count) {
+        do {
+            --current;
+            if (current == invalid)
+                return;
+        } while (!collection.elementMatches(*current));
+    }
+}
+
+template <>
+struct CollectionTraversal<CollectionTraversalType::ChildrenOnly> {
+    using Iterator = ElementChildIterator<Element>;
+
+    static ElementChildIterator<Element> end(ContainerNode& rootNode) { return ElementChildIterator<Element>(rootNode); }
+
+    template <typename CollectionClass>
+    static ElementChildIterator<Element> begin(const CollectionClass&, ContainerNode& rootNode);
+
+    template <typename CollectionClass>
+    static ElementChildIterator<Element> last(const CollectionClass&, ContainerNode& rootNode);
+
+    template <typename CollectionClass>
+    static void traverseForward(const CollectionClass&, ElementChildIterator<Element>& current, unsigned count, unsigned& traversedCount);
+
+    template <typename CollectionClass>
+    static void traverseBackward(const CollectionClass&, ElementChildIterator<Element>& current, unsigned count);
+};
+
+template <typename CollectionClass>
+inline ElementChildIterator<Element> CollectionTraversal<CollectionTraversalType::ChildrenOnly>::begin(const CollectionClass& collection, ContainerNode& rootNode)
+{
+    auto children = childrenOfType<Element>(rootNode);
+    auto end = children.end();
+    for (auto it = children.begin(); it != end; ++it) {
+        if (collection.elementMatches(*it)) {
+            // Drop iterator assertions because HTMLCollections / NodeList use a fine-grained invalidation scheme.
+            it.dropAssertions();
+            return it;
+        }
+    }
+    return end;
+}
+
+template <typename CollectionClass>
+inline ElementChildIterator<Element> CollectionTraversal<CollectionTraversalType::ChildrenOnly>::last(const CollectionClass& collection, ContainerNode& rootNode)
+{
+    auto children = childrenOfType<Element>(rootNode);
+    ElementChildIterator<Element> invalid(collection.rootNode());
+    ElementChildIterator<Element> last(rootNode, children.last());
+    for (auto it = last; it != invalid; --it) {
+        if (collection.elementMatches(*it)) {
+            // Drop iterator assertions because HTMLCollections / NodeList use a fine-grained invalidation scheme.
+            it.dropAssertions();
+            return it;
+        }
+    }
+    return invalid;
+}
+
+template <typename CollectionClass>
+inline void CollectionTraversal<CollectionTraversalType::ChildrenOnly>::traverseForward(const CollectionClass& collection, ElementChildIterator<Element>& current, unsigned count, unsigned& traversedCount)
+{
+    ASSERT(collection.elementMatches(*current));
+    ElementChildIterator<Element> invalid(collection.rootNode());
+    for (traversedCount = 0; traversedCount < count; ++traversedCount) {
+        do {
+            ++current;
+            if (current == invalid)
+                return;
+        } while (!collection.elementMatches(*current));
+    }
+}
+
+template <typename CollectionClass>
+inline void CollectionTraversal<CollectionTraversalType::ChildrenOnly>::traverseBackward(const CollectionClass& collection, ElementChildIterator<Element>& current, unsigned count)
+{
+    ASSERT(collection.elementMatches(*current));
+    ElementChildIterator<Element> invalid(collection.rootNode());
+    for (; count; --count) {
+        do {
+            --current;
+            if (current == invalid)
+                return;
+        } while (!collection.elementMatches(*current));
+    }
+}
+
+template <>
+struct CollectionTraversal<CollectionTraversalType::CustomForwardOnly> {
+    using Iterator = Element*;
+
+    static Element* end(ContainerNode&) { return nullptr; }
+
+    template <typename CollectionClass>
+    static Element* begin(const CollectionClass&, ContainerNode&);
+
+    template <typename CollectionClass>
+    static Element* last(const CollectionClass&, ContainerNode&);
+
+    template <typename CollectionClass>
+    static void traverseForward(const CollectionClass&, Element*& current, unsigned count, unsigned& traversedCount);
+
+    template <typename CollectionClass>
+    static void traverseBackward(const CollectionClass&, Element*&, unsigned count);
+};
+
+template <typename CollectionClass>
+inline Element* CollectionTraversal<CollectionTraversalType::CustomForwardOnly>::begin(const CollectionClass& collection, ContainerNode&)
+{
+    return collection.customElementAfter(nullptr);
+}
+
+template <typename CollectionClass>
+inline Element* CollectionTraversal<CollectionTraversalType::CustomForwardOnly>::last(const CollectionClass&, ContainerNode&)
+{
+    ASSERT_NOT_REACHED();
+    return nullptr;
+}
+
+template <typename CollectionClass>
+inline void CollectionTraversal<CollectionTraversalType::CustomForwardOnly>::traverseForward(const CollectionClass& collection, Element*& current, unsigned count, unsigned& traversedCount)
+{
+    Element* element = current;
+    for (traversedCount = 0; traversedCount < count; ++traversedCount) {
+        element = collection.customElementAfter(element);
+        if (!element) {
+            current = nullptr;
+            return;
+        }
+    }
+    current = element;
+}
+
+template <typename CollectionClass>
+inline void CollectionTraversal<CollectionTraversalType::CustomForwardOnly>::traverseBackward(const CollectionClass&, Element*&, unsigned count)
+{
+    UNUSED_PARAM(count);
+    ASSERT_NOT_REACHED();
+}
+
+} // namespace WebCore