HTML: window.opener clearing

For whatwg/html#4429.

html/browsers/windows/opener-clearing.window.js

@@ -0,0 +1,54 @@
+async_test(t => {
+  // See also https://github.com/whatwg/html/issues/4428
+  const frames = ["iframe", "iframe"].map(val => document.createElement(val));
+  frames[0].srcdoc = "<iframe></iframe>";
+  frames[1].name = "thename";
+  document.body.append(...frames);
+  t.add_cleanup(() => { frames.map(val => val.remove()) });
+  frames[0].onload = t.step_func(() => {
+    const frameWs = frames.map(val => val.contentWindow),
+          deepW = frameWs[0][0]
+          openee = deepW.open("", "thename");
+    assert_equals(openee, frameWs[1]);
+    assert_equals(openee.opener, deepW);
+    frames[0].onload = t.step_func_done(() => {
+      // It'd be interesting to use something like history.back() here that works to see if it's
+      // still null, but that doesn't seem possible.
+      assert_equals(openee.opener, null);
+    });
+    frames[0].srcdoc = "";
+  });
+}, "Set opener browsing context to null when it's in session history");
+
+test(t => {
+  const frames = ["iframe", "iframe"].map(val => document.createElement(val));
+  frames[1].name = "thebettername";
+  document.body.append(...frames);
+  t.add_cleanup(() => { frames.map(val => val.remove()) });
+  const frameWs = frames.map(val => val.contentWindow),
+        openee = frameWs[0].open("", "thebettername");
+  assert_equals(openee, frameWs[1]);
+  assert_equals(openee.opener, frameWs[0]);
+  frames[0].remove();
+  assert_equals(openee.opener, null);
+}, "Set the opener browsing context to null when discarded (<iframe>)");
+
+async_test(t => {
+  // Initially I had one less window.open() call, but Chrome forbids window.open() on about:blank
+  // from creating a new window. This works however.
+  const openee = window.open(),
+        thename = window.open("", "theevenbettername"),
+        furtherOpenee = openee.open("", "theevenbettername");
+  assert_equals(openee.opener, self);
+  assert_equals(furtherOpenee.opener, openee);
+  openee.onunload = t.step_func(() => {
+    assert_equals(furtherOpenee.opener, openee);
+    t.step_timeout(() => {
+      assert_equals(furtherOpenee.opener, null);
+      furtherOpenee.close();
+      t.done();
+    }, 0);
+  });
+  openee.close();
+  assert_equals(furtherOpenee.opener, openee);
+}, "Set the opener browsing context to null when discarded (window.open)");