Switch URL and URLUtils interfaces over to use ScalarValueString.

LayoutTests/fast/domurl/url-pathname.html

Index: LayoutTests/fast/domurl/url-pathname.html
diff --git a/LayoutTests/fast/domurl/url-pathname.html b/LayoutTests/fast/domurl/url-pathname.html
index 080ad972773b5061489766338b75f8bc7054ae31..f5114128f511d8d60ed60f1453c2b40fb4645c3d 100644
--- a/LayoutTests/fast/domurl/url-pathname.html
+++ b/LayoutTests/fast/domurl/url-pathname.html
@@ -51,4 +51,12 @@ test(function() {
     assert_equals(url.href, 'invalid');
 }, 'pathname property invalid URL');
 
+test(function() {
+    var url = new URL('http://www.domain.com/');
+    assert_equals(url.pathname, '/');
+
+    url.pathname = '\udc01\ud802a';
+    assert_equals(url.pathname, '/' + encodeURIComponent('\ufffd\ufffda'));
+}, 'pathname with unmatched surrogates');
+
 </script>