Don't include scroll offset in offsetFromLayoutObject for scrolling contents layers.

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 394 matching lines @@
     if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled()
         && previousPaintInvalidationRect != this->previousPaintInvalidationRect()
         && !usesCompositedScrolling()
         && hasOverflowClip())
         newPaintInvalidationState.setForceSubtreeInvalidationRectUpdateWithinContainer();
 
     newPaintInvalidationState.updateForChildren(reason);
     invalidatePaintOfSubtreesIfNeeded(newPaintInvalidationState);
 }
 
+static bool compositedScrollsWithRespectTo(const LayoutObject* layoutObject, const LayoutBoxModelObject& paintInvalidationContainer)

[wkorman, 2016/05/31 18:34:15]

If layoutObject is never null can use const &?

[chrishtr, 2016/05/31 18:51:54]

It can be null, due to the default parameter of
invalidateDisplayItemClientOnBacking.

+{
+    return paintInvalidationContainer.usesCompositedScrolling() && layoutObject != &paintInvalidationContainer;
+}
+
 void LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRect& r, PaintInvalidationReason invalidationReason, const LayoutObject& object) const
 {
     // TODO(wangxianzhu): Enable the following assert after paint invalidation for spv2 is ready.
     // ASSERT(!RuntimeEnabledFeatures::slimmingPaintV2Enabled());
 
     // https://bugs.webkit.org/show_bug.cgi?id=61159 describes an unreproducible crash here,
     // so assert but check that the layer is composited.
     ASSERT(compositingState() != NotComposited);
 
     // FIXME: generalize accessors to backing GraphicsLayers so that this code is squashing-agnostic.
     if (layer()->groupedMapping()) {
         LayoutRect paintInvalidationRect = r;
         if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer()) {
             // Note: the subpixel accumulation of layer() does not need to be added here. It is already taken into account.
             squashingLayer->setNeedsDisplayInRect(enclosingIntRect(paintInvalidationRect), invalidationReason, object);
         }
+    } else if (compositedScrollsWithRespectTo(&object, *this)) {
+        layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else {
+        // TODO(chrishtr): we should be able to skip scrolling content layers in this case.
         layer()->compositedLayerMapping()->setContentsNeedDisplayInRect(r, invalidationReason, object);
     }
 }
 
-void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClient& displayItemClient, PaintInvalidationReason invalidationReason) const
+void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClient& displayItemClient, PaintInvalidationReason invalidationReason, const LayoutObject* layoutObject) const
 {
     displayItemClient.setDisplayItemsUncached();
 
     // We need to inform the GraphicsLayer about this paint invalidation only when we are tracking
     // paint invalidation or ENABLE(ASSERT).
 #if !ENABLE(ASSERT)
     if (!frameView()->isTrackingPaintInvalidations())
         return;
 #endif
 
     if (layer()->groupedMapping()) {
         if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer())
             squashingLayer->displayItemClientWasInvalidated(displayItemClient, invalidationReason);
     } else if (CompositedLayerMapping* compositedLayerMapping = layer()->compositedLayerMapping()) {
-        compositedLayerMapping->displayItemClientWasInvalidated(displayItemClient, invalidationReason);
+        if (compositedScrollsWithRespectTo(layoutObject, *this))
+            compositedLayerMapping->scrollingDisplayItemClientWasInvalidated(displayItemClient, invalidationReason);
+        else
+            compositedLayerMapping->displayItemClientWasInvalidated(displayItemClient, invalidationReason);
     }
 }
 
 void LayoutBoxModelObject::addOutlineRectsForNormalChildren(Vector<LayoutRect>& rects, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot includeBlockOverflows) const
 {
     for (LayoutObject* child = slowFirstChild(); child; child = child->nextSibling()) {
         // Outlines of out-of-flow positioned descendants are handled in LayoutBlock::addOutlineRects().
         if (child->isOutOfFlowPositioned())
             continue;
 
@@ skipping 656 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink