Add an overload to Object.freeze that preserves literal types

Author: weswigham

src/lib/es5.d.ts

@@ -204,6 +204,12 @@ interface ObjectConstructor {
      */
     freeze<T extends Function>(f: T): T;
 
+    /**
+     * Prevents the modification of existing property attributes and values, and prevents the addition of new properties.
+     * @param o Object on which to lock the attributes.
+     */
+    freeze<T extends {[idx: string]: U | null | undefined | object}, U extends string | number | symbol>(o: T): Readonly<T>;
+
     /**
      * Prevents the modification of existing property attributes and values, and prevents the addition of new properties.
      * @param o Object on which to lock the attributes.