Fix some Closure annotations

Author: aomarks

lib/legacy/legacy-element-mixin.js

@@ -517,6 +517,7 @@ export const LegacyElementMixin = dedupingMixin((base) => {
      * is contained. This is a shorthand for
      * `this.getRootNode().host`.
      * @this {Element}
+     * @return {?Node}
      */
     get domHost() {
       let root = wrap(this).getRootNode();
@@ -940,9 +941,9 @@ export const LegacyElementMixin = dedupingMixin((base) => {
      * Cross-platform helper for setting an element's CSS `translate3d`
      * property.
      *
-     * @param {number} x X offset.
-     * @param {number} y Y offset.
-     * @param {number} z Z offset.
+     * @param {number|string} x X offset.
+     * @param {number|string} y Y offset.
+     * @param {number|string} z Z offset.
      * @param {Element=} node Element to apply the transform to.
      * Defaults to `this`.
      * @return {void}