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

Source/core/layout/compositing/CompositedSelection.h

Index: Source/core/layout/compositing/CompositedSelection.h
diff --git a/Source/core/layout/compositing/CompositedSelection.h b/Source/core/layout/compositing/CompositedSelection.h
index 8a5baa289b95c06d5a3249c7b56bc970f9bc8281..f265d566c3a28d02a51806706287e0da6a904a44 100644
--- a/Source/core/layout/compositing/CompositedSelection.h
+++ b/Source/core/layout/compositing/CompositedSelection.h
@@ -35,6 +35,7 @@
 #include "core/layout/compositing/CompositedSelectionBound.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/graphics/GraphicsLayer.h"
+#include "wtf/Allocator.h"
 
 namespace blink {
 
@@ -42,7 +43,7 @@ namespace blink {
 // end points as well as metadata for the selection region.
 // See |WebSelection|.
 struct CompositedSelection {
-
+    STACK_ALLOCATED();
     CompositedSelection()
         : type(NoSelection)
         , isEditable(false)