Make classes and structures in core/layout fast-allocated.

Source/core/layout/line/WordMeasurement.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All right reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated.
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */
 
 #ifndef WordMeasurement_h
 #define WordMeasurement_h
 
 #include "platform/fonts/SimpleFontData.h"
+#include "wtf/Allocator.h"
 #include "wtf/HashSet.h"
 
 namespace blink {
 
 class WordMeasurement {
+    ALLOW_ONLY_INLINE_ALLOCATION();
 public:
     WordMeasurement()
         : layoutText(nullptr)
         , width(0)
         , startOffset(0)
         , endOffset(0)
     {
     }
 
     LineLayoutText layoutText;
     float width;
     int startOffset;
     int endOffset;
     HashSet<const SimpleFontData*> fallbackFonts;
     FloatRect glyphBounds;
 };
 
 } // namespace blink
 
 #endif // WordMeasurement_h