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

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1392 matching lines @@
     } else {
         // The ancestor layer is also inside the pagination layer, so we need to subtract the visual
         // distance from the ancestor layer to the pagination layer.
         offset.moveBy(-ancestorLayer->visualOffsetFromAncestor(paginationLayer));
     }
     return offset;
 }
 
 void PaintLayer::didUpdateNeedsCompositedScrolling()
 {
+    bool wasSelfPaintingLayer = m_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 != m_isSelfPaintingLayer && m_layoutObject->isFloating())
+        LayoutBlockFlow::setAncestorShouldPaintFloatingObject(*layoutBox(), wasSelfPaintingLayer);
 }
 
 void PaintLayer::updateReflectionInfo(const ComputedStyle* oldStyle)
 {
     ASSERT(!oldStyle || !layoutObject()->style()->reflectionDataEquivalent(oldStyle));
     if (layoutObject()->hasReflection()) {
         ensureRareData().reflectionInfo = adoptPtr(new PaintLayerReflectionInfo(*layoutBox()));
         m_rareData->reflectionInfo->updateAfterStyleChange(oldStyle);
     } else if (m_rareData && m_rareData->reflectionInfo) {
         m_rareData->reflectionInfo->destroy();
@@ skipping 1371 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif