[resource-timing] Test that empty iframes are reported

This CL adds a test that verifies that empty iframes correctly create
a Resource Timing entry.

Bug: 933858
Change-Id: I1d5ae7d8c0fe5fb60ebcf92ebd8f4a51e5fd1d6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2580069Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#835164}

third_party/blink/web_tests/external/wpt/resource-timing/iframe-failed-commit.html

@@ -64,6 +64,16 @@ promise_test(t => {
   return run_test(t, url.toString(), csp_directive);
 }, "Cross-origin iframe that doesn't comply with CSP attribute gets reported");
 
+promise_test(t => {
+  const url = new URL("/resource-timing/resources/200_empty.asis", location.href);
+  return run_test(t, url.toString(), csp_directive);
+}, "Same-origin empty iframe with a 200 status gets reported");
+
+promise_test(t => {
+  const url = new URL("/resource-timing/resources/200_empty.asis", REMOTE_ORIGIN);
+  return run_test(t, url.toString(), csp_directive);
+}, "Cross-origin empty iframe with a 200 status gets reported");
+
 </script>
 </body>
 </html>

third_party/blink/web_tests/external/wpt/resource-timing/resources/200_empty.asis

+HTTP/1.0 200 OK
+Content-Length: 0
+