Add getSanitizeDOMValue to settings API

lib/utils/settings.js

@@ -49,21 +49,30 @@ export const setRootPath = function(path) {
  * `type` indicates where the value is being inserted: one of property, attribute, or text.
  * `node` is the node where the value is being inserted.
  *
- * @type {(function(*,string,string,Node):*)|undefined}
+ * @type {(function(*,string,string,?Node):*)|undefined}
  */
 export let sanitizeDOMValue = window.Polymer && window.Polymer.sanitizeDOMValue || undefined;
 
 /**
  * Sets the global sanitizeDOMValue available via this module's exported
  * `sanitizeDOMValue` variable.
  *
- * @param {(function(*,string,string,Node):*)|undefined} newSanitizeDOMValue the global sanitizeDOMValue callback
+ * @param {(function(*,string,string,?Node):*)|undefined} newSanitizeDOMValue the global sanitizeDOMValue callback
  * @return {void}
  */
 export const setSanitizeDOMValue = function(newSanitizeDOMValue) {
   sanitizeDOMValue = newSanitizeDOMValue;
 };
 
+/**
+ * Gets sanitizeDOMValue, for environments that don't well support `export let`.
+ *
+ * @return {(function(*,string,string,?Node):*)|undefined} sanitizeDOMValue
+ */
+export const getSanitizeDOMValue = function() {
+  return sanitizeDOMValue;
+};
+
 /**
  * Globally settable property to make Polymer Gestures use passive TouchEvent listeners when recognizing gestures.
  * When set to `true`, gestures made from touch will not be able to prevent scrolling, allowing for smoother