Refactors parse_html_subset() into i18n_behavior.

ui/webui/resources/js/parse_html_subset.js

Index: ui/webui/resources/js/parse_html_subset.js
diff --git a/ui/webui/resources/js/parse_html_subset.js b/ui/webui/resources/js/parse_html_subset.js
index ff0df052be215c3c56b12e131cb3d9a80a6daacf..fc255708e2b574f5dd03662482f77e34e0721dbd 100644
--- a/ui/webui/resources/js/parse_html_subset.js
+++ b/ui/webui/resources/js/parse_html_subset.js
@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 /**
- * Parse a very small subset of HTML.  This ensures that insecure HTML /
+ * Parses a very small subset of HTML.  This ensures that insecure HTML /
  * javascript cannot be injected into the new tab page.
  * @param {string} s The string to parse.
  * @param {Array<string>=} opt_extraTags Optional extra allowed tags.
@@ -33,7 +33,7 @@ var parseHtmlSubset = (function() {
    * @type {!Array<string>}
    * @const
    */
-  var allowedTags = ['A', 'B', 'STRONG'];
+  var allowedTags = ['A', 'B', 'SPAN', 'STRONG'];
 
   /** @param {...Object} var_args Objects to merge. */
   function merge(var_args) {