First version of new merge algorithm (not enabled yet)

Source/platform/graphics/paint/SubtreeDisplayItem.h

+// Copyright 2015 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 SubtreeDisplayItem_h
+#define SubtreeDisplayItem_h
+
+#include "platform/geometry/FloatRect.h"
+#include "platform/graphics/paint/DisplayItem.h"
+#include "wtf/Assertions.h"
+
+namespace blink {
+
+class PLATFORM_EXPORT SubtreeCachedDisplayItem : public DisplayItem {
+    WTF_MAKE_FAST_ALLOCATED;
+public:
+    static PassOwnPtr<SubtreeCachedDisplayItem> create(DisplayItemClient client, Type type)
+    {
+        return adoptPtr(new SubtreeCachedDisplayItem(client, type));
+    }
+
+private:
+    SubtreeCachedDisplayItem(DisplayItemClient client, Type type) : DisplayItem(client, type)
+    {
+        ASSERT(isSubtreeCachedType(type));
+    }
+
+    virtual void replay(GraphicsContext*) override final { ASSERT_NOT_REACHED(); }
+    virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override final { ASSERT_NOT_REACHED(); }
+};
+
+class PLATFORM_EXPORT BeginSubtreeDisplayItem : public DisplayItem {
+    WTF_MAKE_FAST_ALLOCATED;
+public:
+    static PassOwnPtr<BeginSubtreeDisplayItem> create(DisplayItemClient client, Type type)
+    {
+        return adoptPtr(new BeginSubtreeDisplayItem(client, type));
+    }
+
+private:
+    BeginSubtreeDisplayItem(DisplayItemClient client, Type type) : DisplayItem(client, type)
+    {
+        ASSERT(isBeginSubtreeType(type));
+    }
+};
+
+class PLATFORM_EXPORT EndSubtreeDisplayItem : public DisplayItem {
+    WTF_MAKE_FAST_ALLOCATED;
+public:
+    static PassOwnPtr<EndSubtreeDisplayItem> create(DisplayItemClient client, Type type)
+    {
+        return adoptPtr(new EndSubtreeDisplayItem(client, type));
+    }
+
+private:
+    EndSubtreeDisplayItem(DisplayItemClient client, Type type) : DisplayItem(client, type)
+    {
+        ASSERT(isEndSubtreeType(type));
+    }
+};
+
+} // namespace blink
+
+#endif // SubtreeDisplayItem_h