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 321 matching lines @@
     // ancestors further.
     if (layer->isSelfPaintingLayer()) {
       DCHECK(!parent() || parent()->m_hasSelfPaintingLayerDescendantDirty ||
              parent()->m_hasSelfPaintingLayerDescendant);
       break;
     }
   }
 }
 
 bool PaintLayer::scrollsWithViewport() const {
-  return (layoutObject()->style()->position() == FixedPosition &&
-          layoutObject()->containerForFixedPosition() ==
-              layoutObject()->view()) ||
-         (layoutObject()->style()->position() == StickyPosition &&
-          !ancestorScrollingLayer());
+  if (layoutObject()->style()->position() == FixedPosition &&

[pdr., 2016/12/06 04:38:51]

Can you move the spv2 codepath outside like so?
if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled()) {
  DCHECK(layoutObject()->paintProperties());
  return layoutObject()
              ->paintProperties()
              ->localBorderBoxProperties()
              ->propertyTreeState.scroll() ==
          layoutObject()
              ->view()
              ->paintProperties()
              ->contentsProperties()
              .propertyTreeState.scroll();
} else {
  return (layoutObject()->style()->position() == FixedPosition &&
          layoutObject()->containerForFixedPosition() ==
              layoutObject()->view()) ||
          (layoutObject()->style()->position() == StickyPosition &&
          !ancestorScrollingLayer());
}

[chrishtr, 2016/12/06 23:56:06]

This isn't quite right, because the method should return whether the PaintLayer
sticks to the viewport of its LayoutView.

+      layoutObject()->containerForFixedPosition() == layoutObject()->view())
+    return true;
+  if (layoutObject()->style()->position() == StickyPosition) {
+    if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled()) {
+      DCHECK(layoutObject()->paintProperties());
+      return layoutObject()
+                 ->paintProperties()
+                 ->localBorderBoxProperties()
+                 ->propertyTreeState.scroll() ==
+             layoutObject()
+                 ->view()
+                 ->paintProperties()
+                 ->contentsProperties()
+                 .propertyTreeState.scroll();
+    } else {
+      return !ancestorScrollingLayer();
+    }
+  }
+  return false;
 }
 
 bool PaintLayer::scrollsWithRespectTo(const PaintLayer* other) const {
   if (scrollsWithViewport() != other->scrollsWithViewport())
     return true;
   return ancestorScrollingLayer() != other->ancestorScrollingLayer();
 }
 
 void PaintLayer::updateLayerPositionsAfterOverflowScroll(
     const DoubleSize& scrollDelta) {
@@ skipping 2894 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif