The element's offset isn't relevant when comparing its dimensions with that of its 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 432 matching lines @@
     return m_frameRect.width() - borderLeft() - borderRight() - verticalScrollbarWidth();
 }
 
 LayoutUnit LayoutBox::clientHeight() const
 {
     return m_frameRect.height() - borderTop() - borderBottom() - horizontalScrollbarHeight();
 }
 
 int LayoutBox::pixelSnappedClientWidth() const
 {
-    return snapSizeToPixel(clientWidth(), location().x() + clientLeft());
+    return snapSizeToPixel(clientWidth(), clientLeft());

[eae, 2016/07/13 20:18:33]

The location is needed to correctly snap the client and offset widths/heights or
it will not match where it is painted.

The width/height does depend on the location. The easiest way to illustrate this
is to imagine a set of repeating inline boxes with a width of 10.5px. Ever other
one will snap to 10px and 11px respectively. This to ensure that the total width
of all of them is as close to (n * 10.5px) as possible.

It is not, however, needed for the overflow rect.

[rhogan, 2016/07/17 18:37:45]

OK, so do we have to live with a scrollbar on this guy?

<div style="top: 87.5px; height: 448.75px; overflow: auto; position: absolute;">
    <div style="height: 449px;">
        <div style="height: 1px; width: 1px;"></div>
    </div>
</div>

 }
 
 int LayoutBox::pixelSnappedClientHeight() const
 {
-    return snapSizeToPixel(clientHeight(), location().y() + clientTop());
+    return snapSizeToPixel(clientHeight(), clientTop());
 }
 
 int LayoutBox::pixelSnappedOffsetWidth(const Element*) const
 {
-    return snapSizeToPixel(offsetWidth(), location().x() + clientLeft());
+    return snapSizeToPixel(offsetWidth(), clientLeft());
 }
 
 int LayoutBox::pixelSnappedOffsetHeight(const Element*) const
 {
-    return snapSizeToPixel(offsetHeight(), location().y() + clientTop());
+    return snapSizeToPixel(offsetHeight(), clientTop());
 }
 
 LayoutUnit LayoutBox::scrollWidth() const
 {
     if (hasOverflowClip())
         return getScrollableArea()->scrollWidth();
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
     if (style()->isLeftToRightDirection())
         return std::max(clientWidth(), layoutOverflowRect().maxX() - borderLeft());
@@ skipping 14 matching lines @@
     return hasOverflowClip() ? LayoutUnit(getScrollableArea()->scrollXOffset()) : LayoutUnit();
 }
 
 LayoutUnit LayoutBox::scrollTop() const
 {
     return hasOverflowClip() ? LayoutUnit(getScrollableArea()->scrollYOffset()) : LayoutUnit();
 }
 
 int LayoutBox::pixelSnappedScrollWidth() const
 {
-    return snapSizeToPixel(scrollWidth(), location().x() + clientLeft());
+    return snapSizeToPixel(scrollWidth(), clientLeft());
 }
 
 int LayoutBox::pixelSnappedScrollHeight() const
 {
     if (hasOverflowClip())
         return snapSizeToPixel(getScrollableArea()->scrollHeight(), location().y() + clientTop());
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
-    return snapSizeToPixel(scrollHeight(), location().y() + clientTop());
+    return snapSizeToPixel(scrollHeight(), clientTop());
 }
 
 void LayoutBox::setScrollLeft(LayoutUnit newLeft)
 {
     // This doesn't hit in any tests, but since the equivalent code in setScrollTop
     // does, presumably this code does as well.
     DisableCompositingQueryAsserts disabler;
 
     if (hasOverflowClip())
         getScrollableArea()->scrollToXOffset(newLeft, ScrollOffsetClamped, ScrollBehaviorAuto);
@@ skipping 4412 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink