Make LayoutFlowThread::fragmentsBoundingBox() faster.

Source/core/layout/LayoutMultiColumnSet.h

 /*
  * Copyright (C) 2012 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 131 matching lines @@
     void expandToEncompassFlowThreadContentsIfNeeded();
 
     void computeIntrinsicLogicalWidths(LayoutUnit& minLogicalWidth, LayoutUnit& maxLogicalWidth) const final;
 
     void attachToFlowThread();
     void detachFromFlowThread();
 
     // The top of the page nearest to the specified block offset. All in flowthread coordinates.
     LayoutUnit pageLogicalTopForOffset(LayoutUnit offset) const;
 
+    LayoutRect fragmentsBoundingBox(const LayoutRect& boundingBoxInFlowThread) const;
+
     void collectLayerFragments(DeprecatedPaintLayerFragments&, const LayoutRect& layerBoundingBox, const LayoutRect& dirtyRect);
 
     LayoutUnit columnGap() const;
 
     // The "CSS actual" value of column-count. This includes overflowing columns, if any.
     unsigned actualColumnCount() const;
 
     const char* name() const override { return "LayoutMultiColumnSet"; }
 
 protected:
@@ skipping 15 matching lines @@
     MultiColumnFragmentainerGroupList m_fragmentainerGroups;
     LayoutFlowThread* m_flowThread;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutMultiColumnSet, isLayoutMultiColumnSet());
 
 } // namespace blink
 
 #endif // LayoutMultiColumnSet_h