Property reconfiguring implemented. Tests added.

src/lookup.cc

Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index 22da70c1ab00697c8669333a5f8609a162dcebb5..672c026c3c7fdc3c30abe9674b940a630d8852e0 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -105,8 +105,10 @@ void LookupIterator::ReconfigureDataProperty(Handle<Object> value,
     PropertyDetails details(attributes, v8::internal::DATA, 0);
     JSObject::SetNormalizedProperty(holder, name(), value, details);
   } else {
-    holder_map_ = Map::ReconfigureDataProperty(holder_map_, descriptor_number(),
-                                               attributes);
+    holder_map_ = Map::ReconfigureExistingProperty(
+        holder_map_, descriptor_number(), i::kData, attributes);
+    holder_map_ =
+        Map::PrepareForDataProperty(holder_map_, descriptor_number(), value);
     JSObject::MigrateToMap(holder, holder_map_);
   }