First version of new merge algorithm (not enabled yet)

Source/core/paint/BlockPainter.cpp

Index: Source/core/paint/BlockPainter.cpp
diff --git a/Source/core/paint/BlockPainter.cpp b/Source/core/paint/BlockPainter.cpp
index fef4a3f30189edd43202c91caaaa04f14aee3a43..fe273b2837b1d2c961cc1ff1a752ba1bb626c009 100644
--- a/Source/core/paint/BlockPainter.cpp
+++ b/Source/core/paint/BlockPainter.cpp
@@ -18,6 +18,7 @@
 #include "core/paint/RenderDrawingRecorder.h"
 #include "core/paint/ScrollRecorder.h"
 #include "core/paint/ScrollableAreaPainter.h"
+#include "core/paint/SubtreeInfoRecorder.h"
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderBlock.h"
 #include "core/rendering/RenderFlexibleBox.h"
@@ -33,6 +34,7 @@ namespace blink {
 void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
     PaintInfo localPaintInfo(paintInfo);
+    SubtreeInfoRecorder subtreeInfoRecorder(paintInfo.context, m_renderBlock, localPaintInfo.phase);
 
     ANNOTATE_GRAPHICS_CONTEXT(localPaintInfo, &m_renderBlock);
 
@@ -51,6 +53,8 @@ void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOff
             return;
     }
 
+    subtreeInfoRecorder.begin();
+
     // There are some cases where not all clipped visual overflow is accounted for.
     // FIXME: reduce the number of such cases.
     ContentsClipBehavior contentsClipBehavior = ForceContentsClip;