More cleanly separate adding from setting elements

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index f5ce1d6c4251ff0582b4ec7fa7d1cb10aea7ff21..25779682733ea78ac3f646c0281405fe2c0ce3cf 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1893,16 +1893,23 @@ class JSObject: public JSReceiver {
   static void SetNormalizedProperty(Handle<JSObject> object, Handle<Name> name,
                                     Handle<Object> value,
                                     PropertyDetails details);
-  static void SetDictionaryElement(Handle<JSObject> object, uint32_t index,
+  static void AddDictionaryElement(Handle<JSObject> object, uint32_t index,
                                    Handle<Object> value,
                                    PropertyAttributes attributes);
-  static void SetSloppyArgumentsElement(Handle<JSObject> object, uint32_t index,
+  static void AddSloppyArgumentsElement(Handle<JSObject> object, uint32_t index,
                                         Handle<Object> value,
                                         PropertyAttributes attributes);
+  static void SetDictionaryElement(Handle<JSObject> object, uint32_t index,
+                                   Handle<Object> value,
+                                   PropertyAttributes attributes);
+  static void SetDictionaryArgumentsElement(Handle<JSObject> object,
+                                            uint32_t index,
+                                            Handle<Object> value,
+                                            PropertyAttributes attributes);
 
-  static void SetFastElement(Handle<JSObject> object, uint32_t index,
+  static void AddFastElement(Handle<JSObject> object, uint32_t index,
                              Handle<Object> value);
-  static void SetFastDoubleElement(Handle<JSObject> object, uint32_t index,
+  static void AddFastDoubleElement(Handle<JSObject> object, uint32_t index,
                                    Handle<Object> value);
 
   static void OptimizeAsPrototype(Handle<JSObject> object,