Adjust background clip when local attachment is used with non-visible overflow.

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 686 matching lines @@
     offset.move(absPos.x(), absPos.y());
     return toIntSize(offset);
 }
 
 FloatQuad LayoutBox::absoluteContentQuad() const
 {
     LayoutRect rect = contentBoxRect();
     return localToAbsoluteQuad(FloatRect(rect));
 }
 
+LayoutRect LayoutBox::backgroundClipRect() const
+{
+    // TODO(flackr): Check for the maximum background clip rect.
+    switch (style()->backgroundClip()) {
+    case BorderFillBox:
+        // A 'border-box' clip on scrollable elements local attachment is treated as 'padding-box'.
+        // https://www.w3.org/TR/css3-background/#the-background-attachment
+        if (!style()->isOverflowVisible() && style()->backgroundLayers().attachment() == LocalBackgroundAttachment)
+            return paddingBoxRect();
+        return borderBoxRect();
+        break;
+    case PaddingFillBox:
+        return paddingBoxRect();
+        break;
+    case ContentFillBox:
+        return contentBoxRect();
+        break;
+    default:
+        break;
+    }
+    return LayoutRect();
+}
+
 void LayoutBox::addOutlineRects(Vector<LayoutRect>& rects, const LayoutPoint& additionalOffset, IncludeBlockVisualOverflowOrNot) const
 {
     rects.append(LayoutRect(additionalOffset, size()));
 }
 
 bool LayoutBox::canResize() const
 {
     // We need a special case for <iframe> because they never have
     // hasOverflowClip(). However, they do "implicitly" clip their contents, so
     // we want to allow resizing them also.
@@ skipping 634 matching lines @@
     // FIXME: Check the opaqueness of background images.
 
     // FIXME: Use rounded rect if border radius is present.
     if (style()->hasBorderRadius())
         return false;
     if (hasClipPath())
         return false;
     // FIXME: The background color clip is defined by the last layer.
     if (style()->backgroundLayers().next())
         return false;
-    LayoutRect backgroundRect;
-    switch (style()->backgroundClip()) {
-    case BorderFillBox:
-        backgroundRect = borderBoxRect();
-        break;
-    case PaddingFillBox:
-        backgroundRect = paddingBoxRect();
-        break;
-    case ContentFillBox:
-        backgroundRect = contentBoxRect();
-        break;
-    default:
-        break;
-    }
-    return backgroundRect.contains(localRect);
+    return backgroundClipRect().contains(localRect);
 }
 
 static bool isCandidateForOpaquenessTest(const LayoutBox& childBox)
 {
     const ComputedStyle& childStyle = childBox.styleRef();
     if (childStyle.position() != StaticPosition && childBox.containingBlock() != childBox.parent())
         return false;
     if (childStyle.visibility() != VISIBLE || childStyle.shapeOutside())
         return false;
     if (childBox.size().isZero())
@@ skipping 3549 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink