Update downloads.jsm to use Downloads.jsm rather than defunct downloads service.

common/modules/promises.jsm

@@ -0,0 +1,48 @@
+// Copyright (c) 2014 Kris Maglione <maglione.k at Gmail>
+//
+// This work is licensed for reuse under an MIT license. Details are
+// given in the LICENSE.txt file included with this file.
+"use strict";
+
+defineModule("promises", {
+    exports: ["Promise", "Task", "promises"],
+    require: []
+});
+
+lazyRequire("resource://gre/modules/Promise.jsm", ["Promise"]);
+lazyRequire("resource://gre/modules/Task.jsm", ["Task"]);
+
+var Promises = Module("Promises", {
+    /**
+     * Wraps the given function so that each call spawns a Task.
+     *
+     * @param {function} fn The function to wrap.
+     * @returns {function}
+     */
+    task: function task(fn) {
+        return function task_(...args) {
+            return Task.spawn(fn.bind.apply(fn, [this].concat(args)));
+        }
+    },
+
+    /**
+     * Wraps the given function so that its first argument is a
+     * callback which, when called, resolves the returned promise.
+     *
+     * @param {function} fn The function to wrap.
+     * @returns {Promise}
+     */
+    withCallback: function withCallback(fn) {
+        return function wrapper(...args) {
+            let deferred = Promise.defer();
+            function callback(arg) {
+                deferred.resolve(arg);
+            }
+            return fn.apply(this, [callback].concat(args));
+        }
+    },
+});
+
+endModule();
+
+// vim: set fdm=marker sw=4 sts=4 ts=8 et ft=javascript: