Correct conversion from flowthread to visual coordinate space when there's border/padding.

third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/MultiColumnFragmentainerGroup.h"
 
 #include "core/layout/ColumnBalancer.h"
 #include "core/layout/FragmentationContext.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 
@@ skipping 92 matching lines @@
     LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
     unsigned columnIndex = columnIndexAtOffset(offsetInFlowThread);
     LayoutRect portionRect(flowThreadPortionRectAt(columnIndex));
     flowThread->flipForWritingMode(portionRect);
     LayoutRect columnRect(columnRectAt(columnIndex));
     m_columnSet.flipForWritingMode(columnRect);
     LayoutSize translationRelativeToGroup = columnRect.location() - portionRect.location();
 
     LayoutSize enclosingTranslation;
     if (LayoutMultiColumnFlowThread* enclosingFlowThread = flowThread->enclosingFlowThread()) {
+        const MultiColumnFragmentainerGroup& firstRow = flowThread->firstMultiColumnSet()->firstFragmentainerGroup();
         // Translation that would map points in the coordinate space of the outermost flow thread to
         // visual points in the first column in the first fragmentainer group (row) in our multicol
         // container.
-        LayoutSize enclosingTranslationOrigin = enclosingFlowThread->flowThreadTranslationAtOffset(flowThread->blockOffsetInEnclosingFragmentationContext());
+        LayoutSize enclosingTranslationOrigin = enclosingFlowThread->flowThreadTranslationAtOffset(firstRow.blockOffsetInEnclosingFragmentationContext());
 
         // Translation that would map points in the coordinate space of the outermost flow thread to
         // visual points in the first column in this fragmentainer group.
         enclosingTranslation = enclosingFlowThread->flowThreadTranslationAtOffset(blockOffsetInEnclosingFragmentationContext());
 
         // What we ultimately return from this method is a translation that maps points in the
         // coordinate space of our flow thread to a visual point in a certain column in this
         // fragmentainer group. We had to go all the way up to the outermost flow thread, since this
         // fragmentainer group may be in a different outer column than the first outer column that
         // this multicol container lives in. It's the visual distance between the first
@@ skipping 404 matching lines @@
     append(MultiColumnFragmentainerGroup(m_columnSet));
     return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups()
 {
     shrink(1);
 }
 
 } // namespace blink