Use the LookupIterator for SetElement and friends

src/elements.h

Index: src/elements.h
diff --git a/src/elements.h b/src/elements.h
index 49faeab0dbd04012b87de6d22067e5cb72040b10..60ff130d2998ce59089567e218ee2716de6cae9b 100644
--- a/src/elements.h
+++ b/src/elements.h
@@ -43,6 +43,11 @@ class ElementsAccessor {
     return HasElement(holder, key, handle(holder->elements()));
   }
 
+  inline Handle<Object> Set(Handle<JSObject> holder, uint32_t key,
+                            Handle<Object> value) {
+    return Set(holder, key, handle(holder->elements()), value);
+  }
+
   // Returns the element with the specified key or undefined if there is no such
   // element. This method doesn't iterate up the prototype chain.  The caller
   // can optionally pass in the backing store to use for the check, which must
@@ -187,6 +192,10 @@ class ElementsAccessor {
                                      uint32_t index) = 0;
   virtual bool HasIndex(FixedArrayBase* backing_store, uint32_t key) = 0;
 
+  virtual Handle<Object> Set(Handle<JSObject> holder, uint32_t key,
+                             Handle<FixedArrayBase> backing_store,
+                             Handle<Object> value) = 0;
+
  private:
   static ElementsAccessor** elements_accessors_;
   const char* name_;