Update should paint flag when a float's composited scrolling status changes

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 290c713268fbc33814d313f91770026ee657b851..fc103e6770a4ea5f1cca562464e71a9e3cf51bae 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -1407,7 +1407,13 @@ LayoutPoint PaintLayer::visualOffsetFromAncestor(const PaintLayer* ancestorLayer
 
 void PaintLayer::didUpdateNeedsCompositedScrolling()
 {
+    bool wasSelfPaintingLayer = isSelfPaintingLayer();
     updateSelfPaintingLayer();
+
+    // If the floating object becomes non-self-painting, so some ancestor should paint it;
+    // if it becomes self-painting, it should paint itself and no ancestor should paint it.
+    if (wasSelfPaintingLayer != isSelfPaintingLayer() && m_layoutObject->isFloating())
+        LayoutBlockFlow::setAncestorShouldPaintFloatingObject(*layoutBox(), wasSelfPaintingLayer);
 }
 
 void PaintLayer::updateReflectionInfo(const ComputedStyle* oldStyle)