diff -r 000000000000 -r 6474c204b198 js/xpconnect/tests/unit/head_watchdog.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/xpconnect/tests/unit/head_watchdog.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,91 @@
+/* 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/. */
+
+//
+// Pref management.
+//
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cu = Components.utils;
+
+var gPrefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
+
+function setWatchdogEnabled(enabled) {
+  gPrefs.setBoolPref("dom.use_watchdog", enabled);
+}
+
+function isWatchdogEnabled() {
+  return gPrefs.getBoolPref("dom.use_watchdog");
+}
+
+//
+// Utilities.
+//
+
+function busyWait(ms) {
+  var start = new Date();
+  while ((new Date()) - start < ms) {}
+}
+
+function do_log_info(aMessage)
+{
+  print("TEST-INFO | " + _TEST_FILE + " | " + aMessage);
+}
+
+// We don't use do_execute_soon, because that inserts a
+// do_test_{pending,finished} pair that gets screwed up when we terminate scripts
+// from the operation callback.
+function executeSoon(fn) {
+  var tm = Cc["@mozilla.org/thread-manager;1"].getService(Ci.nsIThreadManager);
+  tm.mainThread.dispatch({run: fn}, Ci.nsIThread.DISPATCH_NORMAL);
+}
+
+//
+// Asynchronous watchdog diagnostics.
+//
+// When running, the watchdog wakes up every second, and fires the operation
+// callback if the script has been running for >= one second. As such, a script
+// should never be able to run for two seconds or longer without servicing the
+// operation callback. We wait 3 seconds, just to be safe.
+//
+
+function checkWatchdog(expectInterrupt, continuation) {
+  var lastWatchdogWakeup = Cu.getWatchdogTimestamp("WatchdogWakeup");
+  setInterruptCallback(function() {
+    // If the watchdog didn't actually trigger the operation callback, ignore
+    // this call. This allows us to test the actual watchdog behavior without
+    // interference from other sites where we trigger the operation callback.
+    if (lastWatchdogWakeup == Cu.getWatchdogTimestamp("WatchdogWakeup")) {
+      return true;
+    }
+    do_check_true(expectInterrupt);
+    setInterruptCallback(undefined);
+    // Schedule our continuation before we kill this script.
+    executeSoon(continuation);
+    return false;
+  });
+  executeSoon(function() {
+    busyWait(3000);
+    do_check_true(!expectInterrupt);
+    setInterruptCallback(undefined);
+    continuation();
+  });
+}
+
+var gGenerator;
+function continueTest() {
+  gGenerator.next();
+}
+
+function run_test() {
+
+  // Run async.
+  do_test_pending();
+
+  // Instantiate the generator and kick it off.
+  gGenerator = testBody();
+  gGenerator.next();
+}
+