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

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 
 #include "core/frame/Settings.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutScrollbar.h"
@@ skipping 64 matching lines @@
     // not width) but won't invalidate more than expected because in the false-positive case the box must
     // have changed size and have been invalidated.
     const LayoutBoxModelObject& paintInvalidationContainer = paintInvalidationState.paintInvalidationContainer();
     LayoutSize newScrollbarUsedSpaceInBox;
     if (!isOverlay)
         newScrollbarUsedSpaceInBox = newPaintInvalidationRect.size();
     LayoutSize previousScrollbarUsedSpaceInBox;
     if (!previouslyWasOverlay)
         previousScrollbarUsedSpaceInBox= previousPaintInvalidationRect.size();
     if (newScrollbarUsedSpaceInBox != previousScrollbarUsedSpaceInBox)
-        paintInvalidationContainer.invalidateDisplayItemClientOnBacking(box, PaintInvalidationScroll);
+        paintInvalidationContainer.invalidateDisplayItemClientOnBacking(box, PaintInvalidationScroll, &box);
 
     bool invalidated = invalidatePaintOfScrollControlIfNeeded(newPaintInvalidationRect, previousPaintInvalidationRect, needsPaintInvalidation, box, paintInvalidationContainer);
 
     previousPaintInvalidationRect = newPaintInvalidationRect;
     previouslyWasOverlay = isOverlay;
 
     if (!invalidated || !scrollbar || graphicsLayer)
         return;
 
     paintInvalidationContainer.invalidateDisplayItemClientOnBacking(*scrollbar, PaintInvalidationScroll);

[Xianzhu, 2016/05/31 18:27:04]

We should invalidate the scrollbar on container layer. It seems that we'll
invalidate the scrolling layer because a nullptr is passed as the layoutObject.
I think we should force passing the parameter.

[chrishtr, 2016/05/31 18:35:29]

But it has no effect except debugging no? Is this important enough to fix?

[Xianzhu, 2016/05/31 18:43:46]

Oh I forgot my short-cut change and thought we were still invalidate display
item clients through GraphicsLayers.

I think you can leave display item client as-is because it's not clear on which
layer the display item client is invalidated with the current short-cut display
item client invalidation method. I should change how we track display item
client invalidation (maybe one registry for a page or main frame).

     if (scrollbar->isCustomScrollbar())
         toLayoutScrollbar(scrollbar)->invalidateDisplayItemClientsOfScrollbarParts(paintInvalidationContainer);
 }
 
 void PaintInvalidationCapableScrollableArea::invalidatePaintOfScrollControlsIfNeeded(const PaintInvalidationState& paintInvalidationState)
 {
     LayoutBox& box = boxForScrollControlPaintInvalidation();
     invalidatePaintOfScrollbarIfNeeded(horizontalScrollbar(), layerForHorizontalScrollbar(), m_horizontalScrollbarPreviouslyWasOverlay, m_horizontalScrollbarPreviousPaintInvalidationRect, horizontalScrollbarNeedsPaintInvalidation(), box, paintInvalidationState);
     invalidatePaintOfScrollbarIfNeeded(verticalScrollbar(), layerForVerticalScrollbar(), m_verticalScrollbarPreviouslyWasOverlay, m_verticalScrollbarPreviousPaintInvalidationRect, verticalScrollbarNeedsPaintInvalidation(), box, paintInvalidationState);
 
@@ skipping 19 matching lines @@
 
 LayoutRect PaintInvalidationCapableScrollableArea::visualRectForScrollbarParts() const
 {
     LayoutRect fullBounds(m_horizontalScrollbarPreviousPaintInvalidationRect);
     fullBounds.unite(m_verticalScrollbarPreviousPaintInvalidationRect);
     fullBounds.unite(m_scrollCornerAndResizerPreviousPaintInvalidationRect);
     return fullBounds;
 }
 
 } // namespace blink