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 09a2bc91274ddf827d88a4c27e96b9768e1dd6a1..98fa73a871e6e09312254b18555ec3fdda2a8f89 100644
--- a/Source/core/paint/BlockPainter.cpp
+++ b/Source/core/paint/BlockPainter.cpp
@@ -19,6 +19,7 @@
 #include "core/paint/RenderDrawingRecorder.h"
 #include "core/paint/ScrollRecorder.h"
 #include "core/paint/ScrollableAreaPainter.h"
+#include "core/paint/SubtreeRecorder.h"
 #include "core/rendering/PaintInfo.h"
 #include "core/rendering/RenderBlock.h"
 #include "core/rendering/RenderFlexibleBox.h"
@@ -32,6 +33,7 @@ namespace blink {
 
 void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
+    SubtreeRecorder subtreeRecorder(paintInfo.context, m_renderBlock, paintInfo.phase);
     PaintInfo localPaintInfo(paintInfo);
 
     ANNOTATE_GRAPHICS_CONTEXT(localPaintInfo, &m_renderBlock);
@@ -51,6 +53,8 @@ void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOff
             return;
     }
 
+    subtreeRecorder.begin();
+
     // There are some cases where not all clipped visual overflow is accounted for.
     // FIXME: reduce the number of such cases.
     ContentsClipBehavior contentsClipBehavior = ForceContentsClip;