[New Multicolumn] Make offsetLeft, offsetTop and getClientRects() behave.

Source/core/rendering/RenderBox.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 1864 matching lines @@
             LayoutRect columnRect(frameRect());
             block->adjustStartEdgeForWritingModeIncludingColumns(columnRect);
             offset += toSize(columnRect.location());
             LayoutPoint columnPoint = block->flipForWritingModeIncludingColumns(point + offset);
             offset = toLayoutSize(block->flipForWritingModeIncludingColumns(toLayoutPoint(offset)));
             offset += o->columnOffset(columnPoint);
             offset = block->flipForWritingMode(offset);
 
             if (offsetDependsOnPoint)
                 *offsetDependsOnPoint = true;
-        } else
+        } else {
             offset += topLeftLocationOffset();
+            if (o->isRenderFlowThread()) {
+                // So far the point has been in flow thread coordinates (i.e. as if everything in
+                // the fragmentation context lived in one tall single column). Convert it to a
+                // visual point now.
+                LayoutPoint pointInContainer = point + offset;
+                offset += o->columnOffset(pointInContainer);
+                if (offsetDependsOnPoint)
+                    *offsetDependsOnPoint = true;
+            }
+        }
     }
 
     if (o->hasOverflowClip())
         offset -= toRenderBox(o)->scrolledContentOffset();
 
     if (style()->position() == AbsolutePosition && o->isInFlowPositioned() && o->isRenderInline())
         offset += toRenderInline(o)->offsetForInFlowPositionedInline(*this);
 
-    if (offsetDependsOnPoint)
-        *offsetDependsOnPoint |= o->isRenderFlowThread();
-
     return offset;
 }
 
 InlineBox* RenderBox::createInlineBox()
 {
     return new InlineBox(*this);
 }
 
 void RenderBox::dirtyLineBoxes(bool fullLayout)
 {
@@ skipping 2747 matching lines @@
         return 0;
 
     if (!layoutState && !flowThreadContainingBlock())
         return 0;
 
     RenderBlock* containerBlock = containingBlock();
     return containerBlock->offsetFromLogicalTopOfFirstPage() + logicalTop();
 }
 
 } // namespace WebCore