Bug 1606841 [wpt PR 21021] - HTML: attempt to make COEP test less flaky, a=testonly

Automatic update from web-platform-tests
HTML: attempt to make COEP test less flaky

Hopefully addresses https://bugzilla.mozilla.org/show_bug.cgi?id=1605382.

--

wpt-commits: e8fdcbaf22bf28238bb126d84bc960fe9625fe02
wpt-pr: 21021

testing/web-platform/tests/html/cross-origin-embedder-policy/none.https.html

@@ -41,13 +41,13 @@ async_test(t => {
   const w = window.open(`resources/navigate-none.sub.html?to=navigate-require-corp.sub.html`, "window_name");
   t.add_cleanup(() => w.close());
 
-  t.step_timeout(() => {
+  w.onload = t.step_func(() => {
     w.history.back();
     t.step_timeout(() => {
       assert_not_equals(w.document, null);
       t.done();
-    }, 500);
-  }, 500);
+    }, 1500);
+  });
 }, `"none" top-level: navigating a frame back from "require-corp" should succeed`);
 
 async_test(t => {