Statistics of LayoutBox rare data reasons

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 8165be07c17c0a1bc1d635920683fca0955c750e..8ca9e7b88a5f30af7959b5f9750734bbadd0d2b3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -29,6 +29,12 @@
 
 namespace blink {
 
+int paints[9];
+
+int* paintCounts() {
+  return paints;
+}
+
 static inline bool shouldSuppressPaintingLayer(const PaintLayer& layer) {
   // Avoid painting descendants of the root layer when stylesheets haven't
   // loaded. This avoids some FOUC.  It's ok not to draw, because later on, when
@@ -1042,6 +1048,7 @@ void PaintLayerPainter::paintForegroundForFragments(
     clipState = HasClipped;
   }
 
+  size_t sizeBefore = context.getPaintController().newDisplayItemList().size();
   // We have to loop through every fragment multiple times, since we have to
   // issue paint invalidations in each specific phase in order for interleaving
   // of the fragments to work properly.
@@ -1067,6 +1074,8 @@ void PaintLayerPainter::paintForegroundForFragments(
         m_paintLayer.setPreviousPaintPhaseDescendantBlockBackgroundsEmpty(
             phaseIsEmpty);
       }
+    } else {
+      paints[6]++;
     }
 
     if (RuntimeEnabledFeatures::paintUnderInvalidationCheckingEnabled() ||
@@ -1081,6 +1090,8 @@ void PaintLayerPainter::paintForegroundForFragments(
           sizeBefore;
       DCHECK(phaseIsEmpty || m_paintLayer.needsPaintPhaseFloat());
       m_paintLayer.setPreviousPaintPhaseFloatEmpty(phaseIsEmpty);
+    } else {
+      paints[7]++;
     }
 
     paintForegroundForFragmentsWithPhase(PaintPhaseForeground, layerFragments,
@@ -1099,7 +1110,13 @@ void PaintLayerPainter::paintForegroundForFragments(
           sizeBefore;
       DCHECK(phaseIsEmpty || m_paintLayer.needsPaintPhaseDescendantOutlines());
       m_paintLayer.setPreviousPaintPhaseDescendantOutlinesEmpty(phaseIsEmpty);
+    } else {
+      paints[8]++;
     }
+
+    paints[5]++;
+    if (sizeBefore == context.getPaintController().newDisplayItemList().size())
+      paints[4]++;
   }
 }
 
@@ -1114,11 +1131,33 @@ void PaintLayerPainter::paintForegroundForFragmentsWithPhase(
   if (layerFragments.size() > 1)
     cacheSkipper.emplace(context);
 
+  int paintIndex = -1;
+  switch (phase) {
+    case PaintPhaseDescendantBlockBackgroundsOnly:
+      paintIndex = 0;
+      break;
+    case PaintPhaseFloat:
+      paintIndex = 1;
+      break;
+    case PaintPhaseForeground:
+      paintIndex = 2;
+      break;
+    case PaintPhaseDescendantOutlinesOnly:
+      paintIndex = 3;
+      break;
+    default:
+      break;
+  }
+
+  size_t sizeBefore = context.getPaintController().newDisplayItemList().size();
   for (auto& fragment : layerFragments) {
     if (!fragment.foregroundRect.isEmpty())
       paintFragmentWithPhase(phase, fragment, context, fragment.foregroundRect,
                              localPaintingInfo, paintFlags, clipState);
   }
+  if (paintIndex != -1 &&
+      sizeBefore == context.getPaintController().newDisplayItemList().size())
+    paints[paintIndex]++;
 }
 
 void PaintLayerPainter::paintSelfOutlineForFragments(