diff -r 000000000000 -r 6474c204b198 testing/mochitest/tests/SimpleTest/LogController.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/testing/mochitest/tests/SimpleTest/LogController.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,96 @@
+/* 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/. */
+
+var LogController = {}; //create the logger object
+
+LogController.counter = 0; //current log message number
+LogController.listeners = [];
+LogController.logLevel = {
+    FATAL: 50,
+    ERROR: 40,
+    WARNING: 30,
+    INFO: 20,
+    DEBUG: 10
+};
+
+/* set minimum logging level */
+LogController.logLevelAtLeast = function(minLevel) {
+    if (typeof(minLevel) == 'string') {
+        minLevel = LogController.logLevel[minLevel];
+    }
+    return function (msg) {
+        var msgLevel = msg.level;
+        if (typeof(msgLevel) == 'string') {
+            msgLevel = LogController.logLevel[msgLevel];
+        }
+        return msgLevel >= minLevel;
+    };
+};
+
+/* creates the log message with the given level and info */
+LogController.createLogMessage = function(level, info) {
+    var msg = {};
+    msg.num = LogController.counter;
+    msg.level = level;
+    msg.info = info;
+    msg.timestamp = new Date();
+    return msg;
+};
+
+/* helper method to return a sub-array */
+LogController.extend = function (args, skip) {
+    var ret = [];
+    for (var i = skip; i<args.length; i++) {
+        ret.push(args[i]);
+    }
+    return ret;
+};
+
+/* logs message with given level. Currently used locally by log() and error() */
+LogController.logWithLevel = function(level, message/*, ...*/) {
+    var msg = LogController.createLogMessage(
+        level,
+        LogController.extend(arguments, 1)
+    );
+    LogController.dispatchListeners(msg);
+    LogController.counter += 1;
+};
+
+/* log with level INFO */
+LogController.log = function(message/*, ...*/) {
+    LogController.logWithLevel('INFO', message);
+};
+
+/* log with level ERROR */
+LogController.error = function(message/*, ...*/) {
+    LogController.logWithLevel('ERROR', message);
+};
+
+/* send log message to listeners */
+LogController.dispatchListeners = function(msg) {
+    for (var k in LogController.listeners) {
+        var pair = LogController.listeners[k];
+        if (pair.ident != k || (pair[0] && !pair[0](msg))) {
+            continue;
+        }
+        pair[1](msg);
+    }
+};
+
+/* add a listener to this log given an identifier, a filter (can be null) and the listener object */
+LogController.addListener = function(ident, filter, listener) {
+    if (typeof(filter) == 'string') {
+        filter = LogController.logLevelAtLeast(filter);
+    } else if (filter !== null && typeof(filter) !== 'function') {
+        throw new Error("Filter must be a string, a function, or null");
+    }
+    var entry = [filter, listener];
+    entry.ident = ident;
+    LogController.listeners[ident] = entry;
+};
+
+/* remove a listener from this log */
+LogController.removeListener = function(ident) {
+    delete LogController.listeners[ident];
+};