A change in the way we place TransitionElementKinds in the tree.

src/elements-kind.h

Index: src/elements-kind.h
diff --git a/src/elements-kind.h b/src/elements-kind.h
index cb3bb9c9e9fd354efc5f03c90528c17b2ea1ccfe..9bdaf11a35ee30cb135a71c5fe4db620fcd7c248 100644
--- a/src/elements-kind.h
+++ b/src/elements-kind.h
@@ -211,6 +211,12 @@ inline bool IsTransitionableFastElementsKind(ElementsKind from_kind) {
 }
 
 
+// Return the closest fast elements kind that can be transitioned to from both
+// kind1 and kind2. For example, kind1 is a SMI, kind2 is a DOUBLE, then
+// return DOUBLE. If kind1 is a HOLEY_SMI and kind2 is a DOUBLE, return
+// HOLEY_DOUBLE.
+ElementsKind GetUnifiedFastElementsKind(ElementsKind kind1, ElementsKind kind2);
+
 ElementsKind GetNextMoreGeneralFastElementsKind(ElementsKind elements_kind,
                                                 bool allow_only_packed);