Invoke the URL serializer for ErrorEvent.filename

The URL's hash should be included to match majority of browser
engines (WebKit, Gecko, Edge). An "absolute URL" is without the
hash according to the URL standard, but serializing a URL record
includes it by default.

Fixes #2074.
Closes web-platform-tests/wpt#4221.

source

@@ -88020,8 +88020,9 @@ document.querySelector("button").addEventListener("click", bound);
 
    <li>
 
-    <p>Let <var>location</var> be an <span>absolute URL</span> that corresponds to the
-    resource from which <var>script</var> was obtained.</p>
+    <p>Let <var>urlString</var> be the result of applying the <span
+    data-x="concept-url-serializer">URL serializer</span> to the <span>URL record</span> that
+    corresponds to the resource from which <var>script</var> was obtained.</p>
 
     <p class="note">The resource containing the script will typically be the file from which the
     <code>Document</code> was parsed, e.g. for inline <code>script</code> elements or <span>event
@@ -88043,15 +88044,15 @@ document.querySelector("button").addEventListener("click", bound);
    </li>
 
    <li><p>If <var>script</var> has <span>muted errors</span>, then set <var>message</var> to "<code
-   data-x="">Script error.</code>", <var>location</var> to the empty string, <var>line</var> and
+   data-x="">Script error.</code>", <var>urlString</var> to the empty string, <var>line</var> and
    <var>col</var> to 0, and <var>errorValue</var> to null.</p></li>
 
    <li><p>Let <var>notHandled</var> be the result of <span data-x="concept-event-fire">firing an
    event</span> named <code data-x="event-error">error</code> at <var>target</var>, using
    <code>ErrorEvent</code>, with the <code data-x="dom-Event-cancelable">cancelable</code> attribute
    initialized to true, the <code data-x="dom-ErrorEvent-message">message</code> attribute
    initialized to <var>message</var>, the <code data-x="dom-ErrorEvent-filename">filename</code>
-   attribute initialized to <var>location</var>, the <code
+   attribute initialized to <var>urlString</var>, the <code
    data-x="dom-ErrorEvent-lineno">lineno</code> attribute initialized to <var>line</var>, the <code
    data-x="dom-ErrorEvent-colno">colno</code> attribute initialized to <var>col</var>, and the <code
    data-x="dom-ErrorEvent-error">error</code> attribute initialized to
@@ -88108,8 +88109,8 @@ dictionary <dfn>ErrorEventInit</dfn> : <span>EventInit</span> {
   value it was initialized to. It represents the error message.</p>
 
   <p>The <dfn><code data-x="dom-ErrorEvent-filename">filename</code></dfn> attribute must return the
-  value it was initialized to. It represents the <span>absolute URL</span> of the script in which
-  the error originally occurred.</p>
+  value it was initialized to. It represents the <span>URL</span> of the script in which the error
+  originally occurred.</p>
 
   <p>The <dfn><code data-x="dom-ErrorEvent-lineno">lineno</code></dfn> attribute must return the
   value it was initialized to. It represents the line number where the error occurred in the