Implement PaintLayer::scrollsWithViewport for SPv2.

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>
@@ skipping 320 matching lines @@
     // a self-painting descendant in this case, there is no need to dirty our
     // ancestors further.
     if (layer->isSelfPaintingLayer()) {
       DCHECK(!parent() || parent()->m_hasSelfPaintingLayerDescendantDirty ||
              parent()->m_hasSelfPaintingLayerDescendant);
       break;
     }
   }
 }
 
-bool PaintLayer::scrollsWithViewport() const {
+bool PaintLayer::sticksToViewport() const {
+  if (layoutObject()->style()->position() != FixedPosition &&
+      layoutObject()->style()->position() != StickyPosition)
+    return false;
+
+  if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
+    const ScrollPaintPropertyNode* ancestorTargetScrollNode;
+    if (layoutObject()->style()->position() == FixedPosition) {
+      ancestorTargetScrollNode = layoutObject()
+                                     ->view()
+                                     ->paintProperties()
+                                     ->localBorderBoxProperties()
+                                     ->propertyTreeState.scroll();
+    } else {
+      ancestorTargetScrollNode = layoutObject()
+                                     ->view()
+                                     ->paintProperties()
+                                     ->contentsProperties()
+                                     .propertyTreeState.scroll();
+    }
+
+    return layoutObject()
+               ->paintProperties()
+               ->localBorderBoxProperties()
+               ->propertyTreeState.scroll() == ancestorTargetScrollNode;
+  }
+
   return (layoutObject()->style()->position() == FixedPosition &&
           layoutObject()->containerForFixedPosition() ==
               layoutObject()->view()) ||
          (layoutObject()->style()->position() == StickyPosition &&
-          !ancestorScrollingLayer());
+          (!ancestorScrollingLayer() || ancestorScrollingLayer() == root()));

[pdr., 2016/12/07 00:02:05]

Is the new "ancestorScrollingLayer() == root()" check fixing a bug?

[chrishtr, 2016/12/07 01:00:33]

Yes. When root layer scrolling is on, the LayoutView is the scroller, instead
of FrameView. ancestorScrollingLayer() == root() is to handle that.

 }
 
 bool PaintLayer::scrollsWithRespectTo(const PaintLayer* other) const {
-  if (scrollsWithViewport() != other->scrollsWithViewport())
+  if (sticksToViewport() != other->sticksToViewport())
     return true;
   return ancestorScrollingLayer() != other->ancestorScrollingLayer();
 }
 
 void PaintLayer::updateLayerPositionsAfterOverflowScroll(
     const DoubleSize& scrollDelta) {
   clipper().clearClipRectsIncludingDescendants();
   updateLayerPositionsAfterScrollRecursive(scrollDelta,
                                            isPaintInvalidationContainer());
 }
@@ skipping 2890 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif