[builtins] DeleteProperty: Handle last-added fast properties

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 c3bb1399655b36fd9954e08118050ac18584ebbb..900073bdbbc0498b67efcea39d91e133f3cddb26 100644
--- a/test/mjsunit/regress/regress-252797.js
+++ b/test/mjsunit/regress/regress-252797.js
@@ -45,6 +45,7 @@ assertFalse(%HasFastProperties(holder));
 // Create a receiver into dictionary mode.
 var receiver = Object.create(holder, {
   killMe: {value: 0, configurable: true},
+  keepMe: {value: 0, configurable: true}
 });
 delete receiver.killMe;
 assertFalse(%HasFastProperties(receiver));