Painter side preparation for subtree caching

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 c708c8ee63a3e7120256577053fd068462f51870..940e482fcb76f91b9d2620b87b319cde45811234 100644
--- a/Source/core/paint/BlockPainter.cpp
+++ b/Source/core/paint/BlockPainter.cpp
@@ -21,6 +21,7 @@
 #include "core/paint/ScopeRecorder.h"
 #include "core/paint/ScrollRecorder.h"
 #include "core/paint/ScrollableAreaPainter.h"
+#include "core/paint/SubtreeRecorder.h"
 #include "platform/graphics/paint/ClipRecorder.h"
 #include "wtf/Optional.h"
 
@@ -28,6 +29,16 @@ namespace blink {
 
 void BlockPainter::paint(const PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
+    Optional<SubtreeRecorder> subtreeRecorder;
+    // We need to balance the benefit of subtree optimization and the cost of subtree display items.
+    // Only output subtree information if the block has multiple children or multiple line boxes.
+    if ((m_layoutBlock.childrenInline() && m_layoutBlock.lineBoxes() && m_layoutBlock.lineBoxes()->firstLineBox() && m_layoutBlock.lineBoxes()->firstLineBox()->nextLineBox())
+        || (m_layoutBlock.firstChild() && m_layoutBlock.firstChild()->nextSibling())) {
+        subtreeRecorder.emplace(*paintInfo.context, m_layoutBlock, paintInfo.phase);
+        if (subtreeRecorder->canUseCache())
+            return;
+    }
+
     PaintInfo localPaintInfo(paintInfo);
 
     LayoutPoint adjustedPaintOffset = paintOffset + m_layoutBlock.location();