Make sure builtins preserve guarantees about empty element array prototypes.

test/mjsunit/elide-double-hole-check-11.js

Index: test/mjsunit/elide-double-hole-check-11.js
diff --git a/test/mjsunit/elide-double-hole-check-11.js b/test/mjsunit/elide-double-hole-check-11.js
new file mode 100644
index 0000000000000000000000000000000000000000..4603ac0ac5e03d0704509fe7273d21c08bca016a
--- /dev/null
+++ b/test/mjsunit/elide-double-hole-check-11.js
@@ -0,0 +1,16 @@
+// Copyright 2015 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.
+
+// Flags: --allow-natives-syntax
+
+function f1(a, i) {
+  return a[i] + 0.5;
+}
+var arr = [,0.0,2.5];
+assertEquals(0.5, f1(arr, 1));
+assertEquals(0.5, f1(arr, 1));
+%OptimizeFunctionOnNextCall(f1);
+assertEquals(0.5, f1(arr, 1));
+Array.prototype.unshift(1.5);
+assertEquals(2, f1(arr, 0));