diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Source-url.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Source-url.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+// Source.prototype.url can be a string or null.
+
+var g = newGlobal();
+var dbg = new Debugger;
+var gw = dbg.addDebuggee(g);
+for (var fileName of ['file:///var/foo.js', null]) {
+    g.evaluate("function f(x) { return 2*x; }", {fileName: fileName});
+    var fw = gw.getOwnPropertyDescriptor('f').value;
+    assertEq(fw.script.source.url, fileName);
+}