Reland of [builtins] DeleteProperty: Handle last-added fast properties

test/mjsunit/dictionary-properties.js

Index: test/mjsunit/dictionary-properties.js
diff --git a/test/mjsunit/dictionary-properties.js b/test/mjsunit/dictionary-properties.js
index 33360d7f52aac370e049c1d371ab8e1569181825..cffa48547e396727d1d08b00d6d95e3b1fb275bb 100644
--- a/test/mjsunit/dictionary-properties.js
+++ b/test/mjsunit/dictionary-properties.js
@@ -11,6 +11,7 @@ function SlowObject() {
   this.foo = 1;
   this.bar = 2;
   this.qux = 3;
+  this.z = 4;
   delete this.qux;
   assertFalse(%HasFastProperties(this));
 }
@@ -38,6 +39,7 @@ function SlowPrototype() {
 }
 SlowPrototype.prototype.bar = 2;
 SlowPrototype.prototype.baz = 3;
+SlowPrototype.prototype.z = 4;
 delete SlowPrototype.prototype.baz;
 assertFalse(%HasFastProperties(SlowPrototype.prototype));
 var slow_proto = new SlowPrototype;