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diff --git a/webkit/glue/stacking_order_iterator.h b/webkit/glue/stacking_order_iterator.h
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+// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Provides some utilities for iterating over a RenderObject graph in
+// stacking order.
+
+#ifndef WEBKIT_GLUE_STACKING_ORDER_ITERATOR_H__
+#define WEBKIT_GLUE_STACKING_ORDER_ITERATOR_H__
+
+#include <vector>
+
+namespace WebCore {
+class RenderLayer;
+class RenderObject;
+}
+
+// Iterates over a subtree of RenderLayers in stacking order, back to
+// front.  Modifying the RenderObject graph invalidates this iterator.
+//
+// TODO(tulrich): this could go in webkit.
+// TODO(tulrich): needs unittests.
+class RenderLayerIterator {
+ public:
+  RenderLayerIterator();
+
+  // Sets the RenderLayer subtree to iterate over.
+  void Reset(WebCore::RenderLayer* rl);
+
+  // Returns the next RenderLayer in stacking order, back to front.
+  WebCore::RenderLayer* Next();
+ private:
+  class Context {
+   public:
+    Context(WebCore::RenderLayer* layer);
+
+    bool HasMoreNeg();
+    Context NextNeg();
+    bool HasSelf();
+    WebCore::RenderLayer* NextSelf();
+    bool HasMoreOverflow();
+    Context NextOverflow();
+    bool HasMorePos();
+    Context NextPos();
+
+   private:
+    WebCore::RenderLayer* layer_;
+    size_t next_neg_;
+    size_t next_self_;
+    size_t next_overflow_;
+    size_t next_pos_;
+  };
+
+  std::vector<Context> context_stack_;
+};
+
+// Iterates over a subtree of RenderObjects below a given RenderLayer.
+//
+// TODO(tulrich): this could go in webkit.
+// TODO(tulrich): needs unittests.
+class StackingOrderIterator {
+ public:
+  StackingOrderIterator();
+  void Reset(WebCore::RenderLayer* rl);
+  WebCore::RenderObject* Next();
+
+ private:
+  RenderLayerIterator layer_iterator_;
+  WebCore::RenderObject* current_object_;
+  WebCore::RenderObject* current_layer_root_;
+};
+
+#endif  // WEBKIT_GLUE_STACKING_ORDER_ITERATOR_H__