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

Source/core/rendering/RenderMultiColumnSet.cpp

 /*
  * Copyright (C) 2012 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 45 matching lines @@
 
 RenderMultiColumnSet* RenderMultiColumnSet::nextSiblingMultiColumnSet() const
 {
     for (RenderObject* sibling = nextSibling(); sibling; sibling = sibling->nextSibling()) {
         if (sibling->isRenderMultiColumnSet())
             return toRenderMultiColumnSet(sibling);
     }
     return 0;
 }
 
+LayoutSize RenderMultiColumnSet::flowThreadTranslationAtOffset(LayoutUnit blockOffset) const
+{
+    unsigned columnIndex = columnIndexAtOffset(blockOffset);
+    LayoutRect portionRect(flowThreadPortionRectAt(columnIndex));
+    flipForWritingMode(portionRect);
+    LayoutRect columnRect(columnRectAt(columnIndex));
+    flipForWritingMode(columnRect);
+    return contentBoxRect().location() + columnRect.location() - portionRect.location();
+}
+
 LayoutUnit RenderMultiColumnSet::heightAdjustedForSetOffset(LayoutUnit height) const
 {
     RenderBlockFlow* multicolBlock = multiColumnBlockFlow();
     LayoutUnit contentLogicalTop = logicalTop() - multicolBlock->borderBefore() - multicolBlock->paddingBefore();
 
     height -= contentLogicalTop;
     return max(height, LayoutUnit(1)); // Let's avoid zero height, as that would probably cause an infinite amount of columns to be created.
 }
 
 LayoutUnit RenderMultiColumnSet::pageLogicalTopForOffset(LayoutUnit offset) const
@@ skipping 518 matching lines @@
         fragments.append(fragment);
     }
 }
 
 const char* RenderMultiColumnSet::renderName() const
 {
     return "RenderMultiColumnSet";
 }
 
 }