[New Multicolumn] Use the return value from flipForWritingMode().

Source/core/rendering/RenderBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 519 matching lines @@
     bool isDeprecatedFlexItem() const { return !isInline() && !isFloatingOrOutOfFlowPositioned() && parent() && parent()->isDeprecatedFlexibleBox(); }
     bool isFlexItemIncludingDeprecated() const { return !isInline() && !isFloatingOrOutOfFlowPositioned() && parent() && parent()->isFlexibleBoxIncludingDeprecated(); }
 
     virtual LayoutUnit lineHeight(bool firstLine, LineDirectionMode, LinePositionMode = PositionOnContainingLine) const override;
     virtual int baselinePosition(FontBaseline, bool firstLine, LineDirectionMode, LinePositionMode = PositionOnContainingLine) const override;
 
     virtual LayoutUnit offsetLeft() const override;
     virtual LayoutUnit offsetTop() const override;
 
     LayoutPoint flipForWritingModeForChild(const RenderBox* child, const LayoutPoint&) const;
-    LayoutUnit flipForWritingMode(LayoutUnit position) const
+    LayoutUnit flipForWritingMode(LayoutUnit position) const WARN_UNUSED_RETURN
     {
         // The offset is in the block direction (y for horizontal writing modes, x for vertical writing modes).
         if (!UNLIKELY(hasFlippedBlocksWritingMode()))
             return position;
         return logicalHeight() - position;
     }
-    LayoutPoint flipForWritingMode(const LayoutPoint& position) const
+    LayoutPoint flipForWritingMode(const LayoutPoint& position) const WARN_UNUSED_RETURN
     {
         if (!UNLIKELY(hasFlippedBlocksWritingMode()))
             return position;
         return isHorizontalWritingMode() ? LayoutPoint(position.x(), height() - position.y()) : LayoutPoint(width() - position.x(), position.y());
     }
     LayoutPoint flipForWritingModeIncludingColumns(const LayoutPoint&) const;
-    LayoutSize flipForWritingMode(const LayoutSize& offset) const
+    LayoutSize flipForWritingMode(const LayoutSize& offset) const WARN_UNUSED_RETURN
     {
         if (!UNLIKELY(hasFlippedBlocksWritingMode()))
             return offset;
         return isHorizontalWritingMode() ? LayoutSize(offset.width(), height() - offset.height()) : LayoutSize(width() - offset.width(), offset.height());
     }
     void flipForWritingMode(LayoutRect& rect) const
     {
         if (!UNLIKELY(hasFlippedBlocksWritingMode()))
             return;
         if (isHorizontalWritingMode())
             rect.setY(height() - rect.maxY());
         else
             rect.setX(width() - rect.maxX());
     }
-    FloatPoint flipForWritingMode(const FloatPoint& position) const
+    FloatPoint flipForWritingMode(const FloatPoint& position) const WARN_UNUSED_RETURN
     {
         if (!UNLIKELY(hasFlippedBlocksWritingMode()))
             return position;
         return isHorizontalWritingMode() ? FloatPoint(position.x(), height() - position.y()) : FloatPoint(width() - position.x(), position.y());
     }
     void flipForWritingMode(FloatRect& rect) const
     {
         if (!UNLIKELY(hasFlippedBlocksWritingMode()))
             return;
         if (isHorizontalWritingMode())
@@ skipping 224 matching lines @@
         if (UNLIKELY(inlineBoxWrapper() != 0))
             deleteLineBoxWrapper();
     }
 
     ensureRareData().m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace blink
 
 #endif // RenderBox_h