Slimming Paint phase 2 compositing algorithm plumbing & skeleton display list API.

Source/platform/graphics/paint/DisplayList.h

+// Copyright 2014 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.
+
+#ifndef DisplayList_h
+#define DisplayList_h
+
+#include "platform/PlatformExport.h"
+#include "platform/graphics/paint/DisplayItemList.h"
+#include "public/platform/WebDisplayList.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+class DisplayList : public WebDisplayList {
+public:
+    DisplayList(const DisplayItemList& displayItemList) : m_displayItemList(displayItemList) { }
+    unsigned size() const override { return offsets.size(); }
+    const WebDisplayItem& displayItem(unsigned index) const
+    {
+        return *m_displayItemList.displayItems().elementAt(offsets[index]);
+    }
+
+    // This is temporary.
+    const DisplayItem& displayItemInternal(unsigned index) const
+    {
+        return *m_displayItemList.displayItems().elementAt(offsets[index]);
+    }
+    Vector<unsigned> offsets;
+private:
+    const DisplayItemList& m_displayItemList;
+};
+
+} // namespace blink
+
+#endif // DisplayList_h