Use pass by reference in GridItemsSorter

Source/core/rendering/RenderGrid.cpp

 /*
  * Copyright (C) 2011 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 1303 matching lines @@
 
     size_t endGridAreaIndex = std::upper_bound(coordinates.begin() + startGridAreaIndex, coordinates.end() - 1, end) - coordinates.begin();
     if (endGridAreaIndex > 0)
         --endGridAreaIndex;
 
     return GridSpan(startGridAreaIndex, endGridAreaIndex);
 }
 
 class GridItemsSorter {
 public:
-    bool operator()(const std::pair<RenderBox*, size_t> firstChild, const std::pair<RenderBox*, size_t> secondChild) const
+    bool operator()(const std::pair<RenderBox*, size_t>& firstChild, const std::pair<RenderBox*, size_t>& secondChild) const
     {
         if (firstChild.first->style()->order() != secondChild.first->style()->order())
             return firstChild.first->style()->order() < secondChild.first->style()->order();
 
         return firstChild.second < secondChild.second;
     }
 };
 
 void RenderGrid::paintChildren(PaintInfo& paintInfo, const LayoutPoint& paintOffset)
 {
@@ skipping 44 matching lines @@
     if (isOutOfFlowPositioned())
         return "RenderGrid (positioned)";
     if (isAnonymous())
         return "RenderGrid (generated)";
     if (isRelPositioned())
         return "RenderGrid (relative positioned)";
     return "RenderGrid";
 }
 
 } // namespace WebCore