Modified document.open testcase to more accurate for url as USVString type

Modified document.open testcase to more accurate for url as USVString type.
Merging this test in external/wpt where all URL-related test were added
for USVString type.

Bug:
Change-Id: Ie00b677984d973b547b43f6efd47b490ad697fcd
Reviewed-on: https://chromium-review.googlesource.com/836287
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Bhagirathi Satpathy <bhagirathi.s@samsung.com>
Cr-Commit-Position: refs/heads/master@{#525292}
diff --git a/html/dom/usvstring-reflection.html b/html/dom/usvstring-reflection.html
index 04942e0..88feced 100644
--- a/html/dom/usvstring-reflection.html
+++ b/html/dom/usvstring-reflection.html
@@ -18,6 +18,11 @@
 }, "window.open : unpaired surrogate codepoint should be replaced with U+FFFD");
 
 test(() => {
+  var w = document.open("about:blank#\uD800", "", "");
+  assert_equals(w.location.hash, '#%EF%BF%BD');
+}, "document.open : unpaired surrogate codepoint should be replaced with U+FFFD");
+
+test(() => {
   var element = document.createElement("a");
   element.ping = '\uD989';
   assert_equals(element.ping, '\uFFFD');