First version of new merge algorithm (not enabled yet)

Source/core/paint/SubtreeInfoRecorder.h

Index: Source/core/paint/SubtreeInfoRecorder.h
diff --git a/Source/core/paint/SubtreeInfoRecorder.h b/Source/core/paint/SubtreeInfoRecorder.h
new file mode 100644
index 0000000000000000000000000000000000000000..debed2e5c5047432317e8733e3bf3e2d7983e17c
--- /dev/null
+++ b/Source/core/paint/SubtreeInfoRecorder.h
@@ -0,0 +1,46 @@
+// 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 SubtreeInfoRecorder_h
+#define SubtreeInfoRecorder_h
+
+#include "core/rendering/PaintPhase.h"
+#include "wtf/PassOwnPtr.h"
+
+namespace blink {
+
+class DisplayItem;
+class DisplayItemList;
+class GraphicsContext;
+class RenderObject;
+
+// Records subtree information during painting. The recorder's life span covers
+// all painting operations executed during the root of the subtree's paint method
+// for the paint phase.
+class SubtreeInfoRecorder {

[pdr., 2015/02/05 03:35:57]

(Optional) bikeshed: SubtreeRecorder?

[Xianzhu, 2015/02/05 17:57:02]

SubtreeRecorder looks better. Done.

+public:
+    SubtreeInfoRecorder(GraphicsContext*, const RenderObject& root, PaintPhase);
+
+    ~SubtreeInfoRecorder();
+
+    // This method should be called before we actually paint the subtree, then we'll
+    // issue a pair of BeginSubtree/EndSubtree display items to enclose all display
+    // items when we paint the subtree.
+    // Omit this call if we skip painting of the whole subtree (when e.g. the subtree
+    // is out of the viewport, or the whole subtree is not invalidated), then we'll
+    // issue a SubtreeCached display item.
+    void begin();
+
+private:
+    void addDisplayItem(PassOwnPtr<DisplayItem>);
+
+    DisplayItemList* m_displayItemList;
+    const RenderObject& m_subtreeRoot;
+    const PaintPhase m_paintPhase;
+    bool m_begun;
+};
+
+} // namespace blink
+
+#endif // SubtreeInfoRecorder_h