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

Source/core/layout/compositing/CompositedSelection.h

 /*
  * Copyright (C) 2015 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef CompositedSelection_h
 #define CompositedSelection_h
 
 #include "core/editing/SelectionType.h"
 #include "core/layout/compositing/CompositedSelectionBound.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/graphics/GraphicsLayer.h"
+#include "wtf/Allocator.h"
 
 namespace blink {
 
 // The active selection region, containing compositing data for the selection
 // end points as well as metadata for the selection region.
 // See |WebSelection|.
 struct CompositedSelection {
-
+    STACK_ALLOCATED();
     CompositedSelection()
         : type(NoSelection)
         , isEditable(false)
         , isEmptyTextFormControl(false)
     {
     }
 
     SelectionType type;
     CompositedSelectionBound start;
     CompositedSelectionBound end;
     bool isEditable;
     bool isEmptyTextFormControl;
 };
 
 } // namespace blink
 
 #endif // CompositedSelection_h