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

Source/core/layout/LayoutTreeAsText.h

Index: Source/core/layout/LayoutTreeAsText.h
diff --git a/Source/core/layout/LayoutTreeAsText.h b/Source/core/layout/LayoutTreeAsText.h
index 814443c4fab149936efa7404cf35f055e3d97c0e..a7836e72cec01db63e61b417000babe6eba2f495 100644
--- a/Source/core/layout/LayoutTreeAsText.h
+++ b/Source/core/layout/LayoutTreeAsText.h
@@ -28,6 +28,7 @@
 
 #include "core/CoreExport.h"
 #include "platform/text/TextStream.h"
+#include "wtf/Allocator.h"
 #include "wtf/Forward.h"
 
 namespace blink {
@@ -62,6 +63,7 @@ CORE_EXPORT String externalRepresentation(Element*, LayoutAsTextBehavior = Layou
 void write(TextStream&, const LayoutObject&, int indent = 0, LayoutAsTextBehavior = LayoutAsTextBehaviorNormal);
 
 class LayoutTreeAsText {
+    STATIC_ONLY(LayoutTreeAsText);
 // FIXME: This is a cheesy hack to allow easy access to ComputedStyle colors.  It won't be needed if we convert
 // it to use visitedDependentColor instead. (This just involves rebaselining many results though, so for now it's
 // not being done).