Make mapLocalToContainer() work properly for content that follows a column spanner.

Source/core/layout/MultiColumnFragmentainerGroup.cpp

Index: Source/core/layout/MultiColumnFragmentainerGroup.cpp
diff --git a/Source/core/layout/MultiColumnFragmentainerGroup.cpp b/Source/core/layout/MultiColumnFragmentainerGroup.cpp
index 317ec3d63298d46cbe011bf15fb0abd0427b02e1..92dd7d46ba9ff4c71d7c5b722a5f8ef4c042c6f5 100644
--- a/Source/core/layout/MultiColumnFragmentainerGroup.cpp
+++ b/Source/core/layout/MultiColumnFragmentainerGroup.cpp
@@ -132,12 +132,14 @@ void MultiColumnFragmentainerGroup::expandToEncompassFlowThreadOverflow()
 
 LayoutSize MultiColumnFragmentainerGroup::flowThreadTranslationAtOffset(LayoutUnit offsetInFlowThread) const
 {
+    LayoutFlowThread* flowThread = m_columnSet.flowThread();
     unsigned columnIndex = columnIndexAtOffset(offsetInFlowThread);
     LayoutRect portionRect(flowThreadPortionRectAt(columnIndex));
-    m_columnSet.flipForWritingMode(portionRect);
-    LayoutSize translation(translationAtColumn(columnIndex));
-    // TODO(mstensho): need a rectangle (not a point) to flip for writing mode here, once we get support for multiple rows.
-    return toLayoutPoint(translation) - portionRect.location();
+    flowThread->flipForWritingMode(portionRect);
+    LayoutRect columnRect(columnRectAt(columnIndex));
+    m_columnSet.flipForWritingMode(columnRect);
+    LayoutSize translationRelativeToGroup = columnRect.location() - portionRect.location();
+    return translationRelativeToGroup + offsetFromColumnSet() + m_columnSet.topLeftLocationOffset() - flowThread->topLeftLocationOffset();
 }
 
 LayoutUnit MultiColumnFragmentainerGroup::columnLogicalTopForOffset(LayoutUnit offsetInFlowThread) const
@@ -438,23 +440,6 @@ LayoutUnit MultiColumnFragmentainerGroup::calculateColumnHeight(BalancedColumnHe
     return m_columnHeight + m_minSpaceShortage;
 }
 
-LayoutSize MultiColumnFragmentainerGroup::translationAtColumn(unsigned columnIndex) const
-{
-    LayoutUnit logicalTopOffset;
-    LayoutUnit logicalLeftOffset;
-    LayoutUnit columnGap = m_columnSet.columnGap();
-    if (m_columnSet.multiColumnFlowThread()->progressionIsInline()) {
-        logicalLeftOffset = columnIndex * (m_columnSet.pageLogicalWidth() + columnGap);
-        if (!m_columnSet.style()->isLeftToRightDirection())
-            logicalLeftOffset = -logicalLeftOffset;
-    } else {
-        logicalTopOffset = columnIndex * (m_columnHeight + columnGap);
-    }
-
-    LayoutSize offset(logicalLeftOffset, logicalTopOffset);
-    return m_columnSet.isHorizontalWritingMode() ? offset : offset.transposedSize();
-}
-
 LayoutRect MultiColumnFragmentainerGroup::columnRectAt(unsigned columnIndex) const
 {
     LayoutUnit columnLogicalWidth = m_columnSet.pageLogicalWidth();