[runtime] Follow-up fix for "Better encapsulation of dictionary objects...

[runtime] Follow-up fix for "Better encapsulation of dictionary objects handling in lookup iterator."

BUG=chromium:626715

Review-Url: https://codereview.chromium.org/2135253002
Cr-Commit-Position: refs/heads/master@{#37651}

src/lookup.cc

@@ -356,7 +356,11 @@ void LookupIterator::PrepareTransitionToDataProperty(
   state_ = TRANSITION;
   transition_ = transition;
 
-  if (!transition->is_dictionary_map()) {
+  if (transition->is_dictionary_map()) {
+    // Don't set enumeration index (it will be set during value store).
+    property_details_ =
+        PropertyDetails(attributes, i::DATA, 0, PropertyCellType::kNoCell);
+  } else {
     property_details_ = transition->GetLastDescriptorDetails();
     has_property_ = true;
   }

test/mjsunit/regress/regress-crbug-626715.js

+// Copyright 2016 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.
+
+// Create a prototype object which has a lot of fast properties.
+var body = "";
+for (var i = 0; i < 100; i++) {
+  body += `this.a${i} = 0;\n`;
+}
+var Proto = new Function(body);
+
+function A() {}
+A.prototype = new Proto();
+
+// Create a object and add properties that already exist in the prototype.
+// At some point the object will turn into a dictionary mode and one of
+// the fast details from the prototype will be reinterpreted as a details
+// for a new property ...
+var o = new A();
+for (var i = 0; i < 100; i++) {
+  o["a" + i] = i;
+}
+
+// ... which will break the enumeration order of the slow properties.
+var names = Object.getOwnPropertyNames(o);
+for (var i = 0; i < 100; i++) {
+  assertEquals("a" + i, names[i]);
+}