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

Source/core/rendering/RenderMultiColumnFlowThread.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 105 matching lines @@
 
     // FIXME: it's scary that neither destroy() nor the move*Children* methods take care of this,
     // and instead leave you with dangling root line box pointers. But since this is how it is done
     // in other parts of the code that deal with reparenting renderers, let's do the cleanup on our
     // own here as well.
     deleteLineBoxTree();
 
     destroy();
 }
 
+LayoutSize RenderMultiColumnFlowThread::columnOffset(const LayoutPoint& point) const
+{
+    if (!hasValidRegionInfo())
+        return LayoutSize(0, 0);
+
+    LayoutPoint flowThreadPoint(point);
+    flipForWritingMode(flowThreadPoint);
+    LayoutUnit blockOffset = isHorizontalWritingMode() ? flowThreadPoint.y() : flowThreadPoint.x();
+    RenderRegion* renderRegion = regionAtBlockOffset(blockOffset);
+    if (!renderRegion)
+        return LayoutSize(0, 0);
+    return toRenderMultiColumnSet(renderRegion)->flowThreadTranslationAtOffset(blockOffset);
+}
+
 void RenderMultiColumnFlowThread::layoutColumns(bool relayoutChildren, SubtreeLayoutScope& layoutScope)
 {
     // Update the dimensions of our regions before we lay out the flow thread.
     // FIXME: Eventually this is going to get way more complicated, and we will be destroying regions
     // instead of trying to keep them around.
     bool shouldInvalidateRegions = false;
     for (RenderMultiColumnSet* columnSet = firstMultiColumnSet(); columnSet; columnSet = columnSet->nextSiblingMultiColumnSet()) {
         if (relayoutChildren || columnSet->needsLayout()) {
             if (!m_inBalancingPass)
                 columnSet->prepareForLayout();
@@ skipping 149 matching lines @@
 }
 
 bool RenderMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
     if (RenderMultiColumnSet* columnSet = lastMultiColumnSet())
         return columnSet->computedColumnHeight();
     return false;
 }
 
 }