Keep prototype maps in dictionary mode until ICs see them

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 0659268bac2357d5a024ed341218fa2e465a59dc..33360d7f52aac370e049c1d371ab8e1569181825 100644
--- a/test/mjsunit/dictionary-properties.js
+++ b/test/mjsunit/dictionary-properties.js
@@ -39,7 +39,13 @@ function SlowPrototype() {
 SlowPrototype.prototype.bar = 2;
 SlowPrototype.prototype.baz = 3;
 delete SlowPrototype.prototype.baz;
-new SlowPrototype;
+assertFalse(%HasFastProperties(SlowPrototype.prototype));
+var slow_proto = new SlowPrototype;
+// ICs make prototypes fast.
+function ic() { return slow_proto.bar; }
+ic();
+ic();
+assertTrue(%HasFastProperties(slow_proto.__proto__));
 
 // Prototypes stay fast even after deleting properties.
 assertTrue(%HasFastProperties(SlowPrototype.prototype));