Optimistically assume that elements IC only transition once.

src/elements-kind.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 68 matching lines @@
 
 void PrintElementsKind(FILE* out, ElementsKind kind);
 
 ElementsKind GetInitialFastElementsKind();
 
 ElementsKind GetFastElementsKindFromSequenceIndex(int sequence_index);
 
 int GetSequenceIndexFromFastElementsKind(ElementsKind elements_kind);
 
 
+inline bool IsDictionaryElementsKind(ElementsKind kind) {
+  return kind == DICTIONARY_ELEMENTS;
+}
+
+
+inline bool IsExternalArrayElementsKind(ElementsKind kind) {
+  return kind >= FIRST_EXTERNAL_ARRAY_ELEMENTS_KIND &&
+      kind <= LAST_EXTERNAL_ARRAY_ELEMENTS_KIND;
+}
+
+
 inline bool IsFastElementsKind(ElementsKind kind) {
   ASSERT(FIRST_FAST_ELEMENTS_KIND == 0);
   return kind <= FAST_HOLEY_DOUBLE_ELEMENTS;
 }
 
 
 inline bool IsFastDoubleElementsKind(ElementsKind kind) {
   return kind == FAST_DOUBLE_ELEMENTS ||
       kind == FAST_HOLEY_DOUBLE_ELEMENTS;
 }
@@ skipping 102 matching lines @@
     bool allow_only_packed) {
   return IsFastElementsKind(elements_kind) &&
       (elements_kind != TERMINAL_FAST_ELEMENTS_KIND &&
        (!allow_only_packed || elements_kind != FAST_ELEMENTS));
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ELEMENTS_KIND_H_