Always consume user activation when opending a new window

Per whatwg/html#10547, we should always consume the
user activation even if the popup blocker is disabled or the window has
permission to open a new window.

Differential Revision: https://phabricator.services.mozilla.com/D230331

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1930458
gecko-commit: a63ca42b209f7b7eb5d84a897d4f7a6efacbf98c
gecko-reviewers: smaug

html/browsers/windows/consume-user-activation/window-open.html

@@ -15,5 +15,19 @@
     testWin.close();
   });
   assert_false(navigator.userActivation.isActive, "User activation should be consumed");
-});
+}, "Opening a new window should consume user activation");
+
+promise_test(async function(t) {
+  await test_driver.bless("user activation");
+  const testWin = window.open("/resources/blank.html", "testWindow");
+  assert_false(navigator.userActivation.isActive, "User activation should be consumed");
+  t.add_cleanup(() => {
+    testWin.close();
+  });
+
+  // Open the existing window again
+  await test_driver.bless("user activation");
+  const testWin2 = window.open("/resources/blank.html", "testWindow");
+  assert_true(navigator.userActivation.isActive, "User activation should not be consumed");
+}, "Opening an existing window should not consume user activation");
 </script>