Correct flowThreadTranslationAtOffset() for vertical-rl writing mode.

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

Index: third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
diff --git a/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp b/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
index 72000539f6d00ba8935a318a64f18ee079697b88..b992f1ba0e910c7ba857d00ef63beb29217b8327 100644
--- a/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
+++ b/third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.cpp
@@ -110,10 +110,14 @@ LayoutSize MultiColumnFragmentainerGroup::flowThreadTranslationAtOffset(LayoutUn
 
     LayoutRect portionRect(flowThreadPortionRectAt(columnIndex));
     flowThread->flipForWritingMode(portionRect);
+    portionRect.moveBy(flowThread->topLeftLocation());
+
     LayoutRect columnRect(columnRectAt(columnIndex));
+    columnRect.move(offsetFromColumnSet());
     m_columnSet.flipForWritingMode(columnRect);
-    LayoutSize translationRelativeToGroup = columnRect.location() - portionRect.location();
-    LayoutSize translationRelativeToFlowThread = translationRelativeToGroup + offsetFromColumnSet() + m_columnSet.topLeftLocationOffset() - flowThread->topLeftLocationOffset();
+    columnRect.moveBy(m_columnSet.topLeftLocation());
+
+    LayoutSize translationRelativeToFlowThread = columnRect.location() - portionRect.location();
     if (mode == CoordinateSpaceConversion::Containing)
         return translationRelativeToFlowThread;