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

Source/core/layout/svg/SVGTextFragment.h

Index: Source/core/layout/svg/SVGTextFragment.h
diff --git a/Source/core/layout/svg/SVGTextFragment.h b/Source/core/layout/svg/SVGTextFragment.h
index 23544dc6c9239bd5adf742a709628349ea49c100..6e700d766107432f6816f3464d4c454cd4f2255f 100644
--- a/Source/core/layout/svg/SVGTextFragment.h
+++ b/Source/core/layout/svg/SVGTextFragment.h
@@ -21,11 +21,13 @@
 #define SVGTextFragment_h
 
 #include "platform/transforms/AffineTransform.h"
+#include "wtf/Allocator.h"
 
 namespace blink {
 
 // A SVGTextFragment describes a text fragment of a LayoutSVGInlineText which can be laid out at once.
 struct SVGTextFragment {
+    ALLOW_ONLY_INLINE_ALLOCATION();
     SVGTextFragment()
         : characterOffset(0)
         , metricsListOffset(0)