Let mapToVisualRectInAncestorSpace apply ancestor clip if not scrollsOverflow

third_party/WebKit/Source/core/layout/LayoutBox.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, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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 1971 matching lines @@
         // flag on the LayoutObject has been cleared, so use the one on the style().
         topLeft += layer()->offsetForInFlowPosition();
     }
 
     // FIXME: We ignore the lightweight clipping rect that controls use, since if |o| is in mid-layout,
     // its controlClipRect will be wrong. For overflow clip we use the values cached by the layer.
     rect.setLocation(topLeft);
     if (container->hasOverflowClip()) {
         LayoutBox* containerBox = toLayoutBox(container);
         containerBox->mapScrollingContentsRectToBoxSpace(rect);
-        if (container != ancestor && !containerBox->applyOverflowClip(rect, visualRectFlags))
-            return false;
+        if (container != ancestor || !containerBox->scrollsOverflow()) {

[pdr., 2016/04/07 18:23:45]

This block (check hasOverflowClip , mapScrollingContentsRectToBoxSpace, etc) is
repeated 3x verbatim. Can we refactor this logic into a single function,
possibly on LayoutBox?

[Xianzhu, 2016/04/07 19:04:50]

Done.

+            if (!containerBox->applyOverflowClip(rect, visualRectFlags))
+                return false;
+        }
     }
 
     if (ancestorSkipped) {
         // If the ancestor is below o, then we need to map the rect into ancestor's coordinates.
         LayoutSize containerOffset = ancestor->offsetFromAncestorContainer(container);
         rect.move(-containerOffset);
         // If the ancestor is fixed, then the rect is already in its coordinates so doesn't need viewport-adjusting.
         if (ancestor->style()->position() != FixedPosition && container->isLayoutView() && position == FixedPosition)
             toLayoutView(container)->adjustOffsetForFixedPosition(rect);
         return true;
@@ skipping 2699 matching lines @@
 
 void LayoutBox::clearPercentHeightDescendants()
 {
     for (LayoutObject* curr = slowFirstChild(); curr; curr = curr->nextInPreOrder(this)) {
         if (curr->isBox())
             toLayoutBox(curr)->removeFromPercentHeightContainer();
     }
 }
 
 } // namespace blink