fix: don't extend URL in url-shim to support es5 transpilation (#1407)

lighthouse-core/lib/url-shim.js

@@ -31,32 +31,30 @@ URL.INVALID_URL_DEBUG_STRING =
     'Lighthouse was unable to determine the URL of some script executions. ' +
     'It\'s possible a Chrome extension or other eval\'d code is the source.';
 
-class LighthouseURL extends URL {
-  /**
-   * @param {string} url
-   * @return {boolean}
-   */
-  static isValid(url) {
-    try {
-      new URL(url);
-      return true;
-    } catch (e) {
-      return false;
-    }
+/**
+ * @param {string} url
+ * @return {boolean}
+ */
+URL.isValid = function isValid(url) {
+  try {
+    new URL(url);
+    return true;
+  } catch (e) {
+    return false;
   }
+};
 
-  /**
-   * @param {string} urlA
-   * @param {string} urlB
-   * @return {boolean}
-   */
-  static hostsMatch(urlA, urlB) {
-    try {
-      return new URL(urlA).host === new URL(urlB).host;
-    } catch (e) {
-      return false;
-    }
+/**
+ * @param {string} urlA
+ * @param {string} urlB
+ * @return {boolean}
+ */
+URL.hostsMatch = function hostsMatch(urlA, urlB) {
+  try {
+    return new URL(urlA).host === new URL(urlB).host;
+  } catch (e) {
+    return false;
   }
-}
+};
 
-module.exports = LighthouseURL;
+module.exports = URL;