[runtime] Object.create(null) creates a slow object

test/mjsunit/regress/regress-252797.js

Index: test/mjsunit/regress/regress-252797.js
diff --git a/test/mjsunit/regress/regress-252797.js b/test/mjsunit/regress/regress-252797.js
index 379205f59930776337c75d4e925bd56439d3c539..ac776a17d88496963f797d342c681d5c53f25681 100644
--- a/test/mjsunit/regress/regress-252797.js
+++ b/test/mjsunit/regress/regress-252797.js
@@ -31,11 +31,17 @@
 // starting with a negative lookup.
 
 // Create a holder in fast mode.
-var holder = Object.create(null, {
+var holder = Object.create({}, {
   holderMethod: {value: function() {}}
 });
 assertTrue(%HasFastProperties(holder));
 
+// We assume dict usage for null prototype.
+var holder = Object.create(null, {
+  holderMethod: {value: function() {}}
+});
+assertFalse(%HasFastProperties(holder));
+
 // Create a receiver into dictionary mode.
 var receiver = Object.create(holder, {
   killMe: {value: 0, configurable: true},