Use more robust way to keep the timer reference alive.

Strict mode generates a warning about |timer;| being a useless
expression, which suggest that this might be optimized away at some
point (see also https://bugzil.la/640629#c9). Instead, explicitly
store the timer in the observer object.
const EXPORTED_SYMBOLS = ['timeout'];

function timeout(aCallback, aDelay) {
  // Create the timer object.
  var timer = Components.classes["@mozilla.org/timer;1"]
      .createInstance(Components.interfaces.nsITimer);

  // The timer object may be garbage collected before it fires, so we need to
  // keep a reference to it alive (https://bugzil.la/647998).
  // However, simply creating a closure over the timer object without using it
  // may not be enough, as the timer might get optimized out of the closure
  // scope (https://bugzil.la/640629#c9). To work around this, the timer object
  // is explicitly stored as a property of the observer.
  var observer = {
    'observe': function() {
      delete observer.timer;
      aCallback();
    },
    'timer': timer
  };

  timer.init(observer, aDelay, Components.interfaces.nsITimer.TYPE_ONE_SHOT);
}

Components.utils.import('resource://greasemonkey/util.js');

const EXPORTED_SYMBOLS = ['timeout'];

function timeout(aCallback, aDelay, aType) {
  var type = aType;
  if ('undefined' == typeof type) {
    type = Components.interfaces.nsITimer.TYPE_ONE_SHOT;
  }

  // Create the timer object.
  var timer = Components.classes["@mozilla.org/timer;1"]
      .createInstance(Components.interfaces.nsITimer);
  // Init the callback, with a closure reference to the timer, so that it is
  // not garbage collected before it fires.
  timer.init(
      {
        'observe': function() {
          timer;  // Here's the reference that keeps the timer alive!
          aCallback();
        }
      },
      aDelay, type);
}
