Use LookupIterator to transition to accessors

src/v8natives.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.
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Object = global.Object;
 // var $Boolean = global.Boolean;
 // var $Number = global.Number;
 // var $Function = global.Function;
@@ skipping 822 matching lines @@
     }
 
     %DefineDataPropertyUnchecked(obj, p, value, flag);
   } else {
     // There are 3 cases that lead here:
     // Step 4b - defining a new accessor property.
     // Steps 9c & 12 - replacing an existing data property with an accessor
     //                 property.
     // Step 12 - updating an existing accessor property with an accessor
     //           descriptor.
-    var getter = desc.hasGetter() ? desc.getGet() : null;
-    var setter = desc.hasSetter() ? desc.getSet() : null;
+    var getter = null;
+    if (desc.hasGetter()) {
+      getter = desc.getGet();
+    } else if (IsAccessorDescriptor(current) && current.hasGetter()) {
+      getter = current.getGet();
+    }
+    var setter = null;
+    if (desc.hasSetter()) {
+      setter = desc.getSet();
+    } else if (IsAccessorDescriptor(current) && current.hasSetter()) {
+      setter = current.getSet();
+    }
     %DefineAccessorPropertyUnchecked(obj, p, getter, setter, flag);
   }
   return true;
 }
 
 
 // ES5 section 15.4.5.1.
 function DefineArrayProperty(obj, p, desc, should_throw) {
   // Note that the length of an array is not actually stored as part of the
   // property, hence we use generated code throughout this function instead of
@@ skipping 1046 matching lines @@
   }
   if (!IS_SPEC_FUNCTION(method)) {
     throw MakeTypeError('not_iterable', [obj]);
   }
   var iterator = %_CallFunction(obj, method);
   if (!IS_SPEC_OBJECT(iterator)) {
     throw MakeTypeError('not_an_iterator', [iterator]);
   }
   return iterator;
 }