Fix DOMPurify on webOS 1.2

DOMParser.createHTMLDocument on webOS 1.2 (WebKit) doesn't
support 'text/html' - polyfill it.

src/legacy/domParserTextHtml.js

@@ -0,0 +1,36 @@
+/*
+ * DOMParser HTML extension
+ * 2019-11-13
+ *
+ * By Eli Grey, http://eligrey.com
+ * Public domain.
+ * NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
+ */
+
+/*! @source https://gist.github.com/1129031 */
+
+(function (DOMParser) {
+    'use strict';
+
+    const DOMParser_proto = DOMParser.prototype;
+    const real_parseFromString = DOMParser_proto.parseFromString;
+
+    // Firefox/Opera/IE throw errors on unsupported types
+    try {
+        // WebKit returns null on unsupported types
+        if ((new DOMParser).parseFromString('', 'text/html')) {
+            // text/html parsing is natively supported
+            return;
+        }
+    } catch (ex) { /* noop */ }
+
+    DOMParser_proto.parseFromString = function (markup, type) {
+        if (/^\s*text\/html\s*(?:;|$)/i.test(type)) {
+            const doc = document.implementation.createHTMLDocument('');
+            doc.documentElement.innerHTML = markup;
+            return doc;
+        } else {
+            return real_parseFromString.apply(this, arguments);
+        }
+    };
+}(DOMParser));