Apply offset from the correct graphics layer; simplify code for link highlights.

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 530 matching lines @@
   if (m_rareData)
     m_rareData->enclosingPaginationLayer = nullptr;
   for (PaintLayer* child = firstChild(); child; child = child->nextSibling())
     child->clearPaginationRecursive();
 }
 
 void PaintLayer::mapPointInPaintInvalidationContainerToBacking(
     const LayoutBoxModelObject& paintInvalidationContainer,
     FloatPoint& point) {
   PaintLayer* paintInvalidationLayer = paintInvalidationContainer.layer();
-  if (!paintInvalidationLayer->groupedMapping()) {
-    point.move(paintInvalidationLayer->compositedLayerMapping()
-                   ->contentOffsetInCompositingLayer());

[Xianzhu, 2016/12/29 05:48:12]

Was confused by this when working on VisualRectMappingTest for spinvalidation.
Glad to see this gone.

[Xianzhu, 2016/12/29 06:33:00]

I just paused CQ because of a question:

Is there any caller depending on the behavior of the above removed lines?

- Many callers like the following seem fine:
  if (paintInvalidationContainer.layer()->groupedMapping())
    mapPointInPaintInvalidationContainerToBacking(...)

- LinkHighlightImpl should expect the behavior change;

- I'm not sure about LayoutObject::localToInvalidationBackingPoint(). One
callsite is FrameView::computeCompositedSelection(). Can you verify if the
behavior change for these callsites are OK?

Also we may need a followup to also remove the similar offset in
mapRectInPaintInvalidationContainerToBacking(), verify callsites, and (maybe
optionally) simplify callsites by removing the redundant groupdMapping() check.

[chrishtr, 2016/12/29 16:53:04]

This one is not ok. Re-inserted this line. As you mention, only one call
site triggers this after my patch.
Will follow up with other patches along these lines.

+  if (!paintInvalidationLayer->groupedMapping())
     return;
-  }
 
   LayoutBoxModelObject* transformedAncestor =
       paintInvalidationLayer->enclosingTransformedAncestor()->layoutObject();
   if (!transformedAncestor)
     return;
 
   // |paintInvalidationContainer| may have a local 2D transform on it, so take
   // that into account when mapping into the space of the transformed ancestor.
   point = paintInvalidationContainer.localToAncestorPoint(point,
                                                           transformedAncestor);
@@ skipping 2682 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif