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diff --git a/Source/WebCore/accessibility/AccessibilityTree.cpp b/Source/WebCore/accessibility/AccessibilityTree.cpp
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+++ b/Source/WebCore/accessibility/AccessibilityTree.cpp
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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.
+ * 3.  Neither the name of Apple Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE 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 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.
+ */
+
+#include "config.h"
+#include "AccessibilityTree.h"
+
+#include "AXObjectCache.h"
+#include "AccessibilityTreeItem.h"
+#include "Element.h"
+#include "HTMLNames.h"
+
+#include <wtf/Deque.h>
+
+namespace WebCore {
+
+using namespace HTMLNames;
+    
+AccessibilityTree::AccessibilityTree(RenderObject* renderer)
+    : AccessibilityRenderObject(renderer)
+{
+}
+    
+AccessibilityTree::~AccessibilityTree()
+{
+}
+    
+Ref<AccessibilityTree> AccessibilityTree::create(RenderObject* renderer)
+{
+    return adoptRef(*new AccessibilityTree(renderer));
+}
+    
+bool AccessibilityTree::computeAccessibilityIsIgnored() const
+{
+    return accessibilityIsIgnoredByDefault();
+}
+
+AccessibilityRole AccessibilityTree::determineAccessibilityRole()
+{
+    if ((m_ariaRole = determineAriaRoleAttribute()) != TreeRole)
+        return AccessibilityRenderObject::determineAccessibilityRole();
+
+    return isTreeValid() ? TreeRole : GroupRole;
+}
+
+bool AccessibilityTree::nodeHasTreeItemChild(Node& node) const
+{
+    for (auto* child = node.firstChild(); child; child = child->nextSibling()) {
+        if (nodeHasRole(child, "treeitem"))
+            return true;
+    }
+    return false;
+}
+
+bool AccessibilityTree::isTreeValid() const
+{
+    // A valid tree can only have treeitem or group of treeitems as a child
+    // http://www.w3.org/TR/wai-aria/roles#tree
+
+    Node* node = this->node();
+    if (!node)
+        return false;
+    
+    Deque<Node*> queue;
+    for (auto* child = node->firstChild(); child; child = child->nextSibling())
+        queue.append(child);
+
+    while (!queue.isEmpty()) {
+        auto child = queue.takeFirst();
+
+        if (!is<Element>(*child))
+            continue;
+        if (nodeHasRole(child, "treeitem"))
+            continue;
+        if (nodeHasRole(child, "presentation")) {
+            if (!nodeHasTreeItemChild(*child))
+                return false;
+            continue;
+        }
+        if (!nodeHasRole(child, "group"))
+            return false;
+
+        for (auto* groupChild = child->firstChild(); groupChild; groupChild = groupChild->nextSibling())
+            queue.append(groupChild);
+    }
+    return true;
+}
+
+} // namespace WebCore