Change SmartMove no-op behavior to match SimpleMove (and ES6 spec)

src/array.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 "use strict";
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Array = global.Array;
 
@@ skipping 216 matching lines @@
         }
       }
     }
   }
 }
 
 
 // This function implements the optimized splice implementation that can use
 // special array operations to handle sparse arrays in a sensible fashion.
 function SmartMove(array, start_i, del_count, len, num_additional_args) {
+  // Bail out if no moving is necessary.
+  if (num_additional_args === del_count) return;
   // Move data to new array.
   var new_array = new InternalArray(len - del_count + num_additional_args);
   var indices = %GetArrayKeys(array, len);
   if (IS_NUMBER(indices)) {
     var limit = indices;
     for (var i = 0; i < start_i && i < limit; ++i) {
       var current = array[i];
       if (!IS_UNDEFINED(current) || i in array) {
         new_array[i] = current;
       }
@@ skipping 1319 matching lines @@
   ));
 
   SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();