Move Command's property definitions outside init.

--HG--
extra : rebase_source : 2237c2350957975938140d4f4c556898763ef7d3

common/content/util.js

@@ -805,6 +805,15 @@ const Util = Module("util", {
             return obj;
         },
 
+        /**
+         * Compacts an array, removing all elements that are null or undefined:
+         *    ["foo", null, "bar", undefined] -> ["foo", "bar"]
+         *
+         * @param {Array} ary
+         * @returns {Array}
+         */
+        compact: function compact(ary) ary.filter(function (item) item != null),
+
         /**
          * Flattens an array, such that all elements of the array are
          * joined into a single array: