diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/testDateNow.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/testDateNow.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+function testDateNow() {
+    // Accessing global.Date for the first time will change the global shape,
+    // so do it before the loop starts; otherwise we have to loop an extra time
+    // to pick things up.
+    var time = Date.now();
+    for (var j = 0; j < 9; ++j)
+        time = Date.now();
+    return "ok";
+}
+assertEq(testDateNow(), "ok");