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

Source/core/layout/svg/SVGTextLayoutEngineSpacing.h

Index: Source/core/layout/svg/SVGTextLayoutEngineSpacing.h
diff --git a/Source/core/layout/svg/SVGTextLayoutEngineSpacing.h b/Source/core/layout/svg/SVGTextLayoutEngineSpacing.h
index 9cedfd81ed715b2c20fae19a422eaf57de91e0e1..e69c5a1a3708909ed2705fb70849790f666921f2 100644
--- a/Source/core/layout/svg/SVGTextLayoutEngineSpacing.h
+++ b/Source/core/layout/svg/SVGTextLayoutEngineSpacing.h
@@ -20,6 +20,7 @@
 #ifndef SVGTextLayoutEngineSpacing_h
 #define SVGTextLayoutEngineSpacing_h
 
+#include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/Unicode.h"
 
@@ -29,6 +30,7 @@ class Font;
 
 // Helper class used by SVGTextLayoutEngine to handle 'letter-spacing' and 'word-spacing'.
 class SVGTextLayoutEngineSpacing {
+    STACK_ALLOCATED();
     WTF_MAKE_NONCOPYABLE(SVGTextLayoutEngineSpacing);
 public:
     SVGTextLayoutEngineSpacing(const Font&, float effectiveZoom);