Remove clips where we can show that they are unnecessary.

Source/core/rendering/RenderBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 160 matching lines @@
 
     // Visual and layout overflow are in the coordinate space of the box.  This means that they aren't purely physical directions.
     // For horizontal-tb and vertical-lr they will match physical directions, but for horizontal-bt and vertical-rl, the top/bottom and left/right
     // respectively are flipped when compared to their physical counterparts.  For example minX is on the left in vertical-lr,
     // but it is on the right in vertical-rl.
     LayoutRect layoutOverflowRect() const { return m_overflow ? m_overflow->layoutOverflowRect() : clientBoxRect(); }
     IntRect pixelSnappedLayoutOverflowRect() const { return pixelSnappedIntRect(layoutOverflowRect()); }
     LayoutSize maxLayoutOverflow() const { return LayoutSize(layoutOverflowRect().maxX(), layoutOverflowRect().maxY()); }
     LayoutUnit logicalLeftLayoutOverflow() const { return style()->isHorizontalWritingMode() ? layoutOverflowRect().x() : layoutOverflowRect().y(); }
     LayoutUnit logicalRightLayoutOverflow() const { return style()->isHorizontalWritingMode() ? layoutOverflowRect().maxX() : layoutOverflowRect().maxY(); }
-    
+
     virtual LayoutRect visualOverflowRect() const { return m_overflow ? m_overflow->visualOverflowRect() : borderBoxRect(); }
     LayoutUnit logicalLeftVisualOverflow() const { return style()->isHorizontalWritingMode() ? visualOverflowRect().x() : visualOverflowRect().y(); }
     LayoutUnit logicalRightVisualOverflow() const { return style()->isHorizontalWritingMode() ? visualOverflowRect().maxX() : visualOverflowRect().maxY(); }
 
     LayoutRect overflowRectForPaintRejection() const;
-    
+
     void addLayoutOverflow(const LayoutRect&);
-    void addVisualOverflow(const LayoutRect&);
-    
+
+    enum VisualOverflowClipBehavior { VisualOverflowNotClipped, VisualOverflowClippedByContentsClip };
+    virtual void addVisualOverflow(const LayoutRect&, VisualOverflowClipBehavior);

[Julien - ping for review, 2013/06/19 19:42:58]

Making this virtual seems to go in the wrong direction. This is required mainly
because you are storing the new rect in RenderBlock where any RenderBox can have
an overflow clip but not all are blocks (e.g. RenderListMarkers).

[jbroman, 2013/08/02 14:28:17]

I don't see how any other kind of box can have an overflow clip (certainly I
can't think of a way to apply an overflow clip to a list marker).

In particular, the only implementation of hasOverflowClip() is in RenderObject,
which queries the bit fields. The only invocation of setHasOverflowClip where
the argument can be true is in RenderBox::updateFromStyle, where it is guarded
by the condition isRenderBlock().

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

Equivalently, the eponymous "overflow" CSS property applies only to block
container elements (which always have renderers which subclass RenderBlock,
AFAICT).

http://www.w3.org/TR/CSS2/visufx.html#overflow

I did originally have the rect in RenderBox, but it was only used for
RenderBlocks, so that seemed silly to penalize ALL boxes everywhere with the
size (including, as you note, list markers, as well as blocks with no overflow
clip).

+
     void addVisualEffectOverflow();
     void addOverflowFromChild(RenderBox* child) { addOverflowFromChild(child, child->locationOffset()); }
     void addOverflowFromChild(RenderBox* child, const LayoutSize& delta);
     void clearLayoutOverflow();
-    
+
     void updateLayerTransform();
 
     LayoutUnit contentWidth() const { return clientWidth() - paddingLeft() - paddingRight(); }
     LayoutUnit contentHeight() const { return clientHeight() - paddingTop() - paddingBottom(); }
     LayoutUnit contentLogicalWidth() const { return style()->isHorizontalWritingMode() ? contentWidth() : contentHeight(); }
     LayoutUnit contentLogicalHeight() const { return style()->isHorizontalWritingMode() ? contentHeight() : contentWidth(); }
 
     // IE extensions. Used to calculate offsetWidth/Height.  Overridden by inlines (RenderFlow)
     // to return the remaining width on a given line (and the height of a single line).
     virtual LayoutUnit offsetWidth() const { return width(); }
@@ skipping 253 matching lines @@
     
     bool hasUnsplittableScrollingOverflow() const;
     bool isUnsplittableForPagination() const;
 
     virtual LayoutRect localCaretRect(InlineBox*, int caretOffset, LayoutUnit* extraWidthToEndOfLine = 0);
 
     virtual LayoutRect overflowClipRect(const LayoutPoint& location, RenderRegion*, OverlayScrollbarSizeRelevancy = IgnoreOverlayScrollbarSize);
     LayoutRect clipRect(const LayoutPoint& location, RenderRegion*);
     virtual bool hasControlClip() const { return false; }
     virtual LayoutRect controlClipRect(const LayoutPoint&) const { return LayoutRect(); }
-    bool pushContentsClip(PaintInfo&, const LayoutPoint& accumulatedOffset);
+    bool pushContentsClip(PaintInfo&, const LayoutPoint& accumulatedOffset, const LayoutRect* visualOverflowRect = 0);
     void popContentsClip(PaintInfo&, PaintPhase originalPhase, const LayoutPoint& accumulatedOffset);
 
     virtual void paintObject(PaintInfo&, const LayoutPoint&) { ASSERT_NOT_REACHED(); }
     virtual void paintBoxDecorations(PaintInfo&, const LayoutPoint&);
     virtual void paintMask(PaintInfo&, const LayoutPoint&);
     virtual void imageChanged(WrappedImagePtr, const IntRect* = 0);
 
     // Called when a positioned object moves but doesn't necessarily change size.  A simplified layout is attempted
     // that just updates the object's position. If the size does change, the object remains dirty.
     bool tryLayoutDoingPositionedMovementOnly()
@@ skipping 256 matching lines @@
         if (UNLIKELY(m_inlineBoxWrapper != 0))
             deleteLineBoxWrapper();
     }
 
     m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace WebCore
 
 #endif // RenderBox_h