diff -r 000000000000 -r 6474c204b198 js/src/jit-test/lib/referencesVia.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/lib/referencesVia.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,30 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function referencesVia(from, edge, to) {
+    if (typeof findReferences !== 'function')
+        return true;
+
+    edge = "edge: " + edge;
+    var edges = findReferences(to);
+    if (edge in edges && edges[edge].indexOf(from) != -1)
+        return true;
+
+    // Be nice: make it easy to fix if the edge name has just changed.
+    var alternatives = [];
+    for (var e in edges) {
+        if (edges[e].indexOf(from) != -1)
+            alternatives.push(e);
+    }
+    if (alternatives.length == 0) {
+        print("referent not referred to by referrer after all");
+    } else {
+        print("referent is not referenced via: " + uneval(edge));
+        print("but it is referenced via:       " + uneval(alternatives));
+    }
+    print("all incoming edges, from any object:");
+    for (var e in edges)
+        print(e);
+    return false;
+}