Bug 1740043 - Add fullscreen test; r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D131007

dom/html/test/browser.ini

@@ -34,6 +34,8 @@ tags = fullscreen
 support-files = file_fullscreen-newtab.html
 skip-if = os == 'mac'
   (os == 'linux' && bits == 64 && os_version == '18.04')  # Bug 1601460, Bug 1494843
+[browser_fullscreen-navigation.js]
+tags = fullscreen
 [browser_submission_flush.js]
 [browser_refresh_after_document_write.js]
 support-files =

dom/html/test/browser_fullscreen-navigation.js

@@ -0,0 +1,64 @@
+"use strict";
+
+// This test tends to trigger a race in the fullscreen time telemetry,
+// where the fullscreen enter and fullscreen exit events (which use the
+// same histogram ID) overlap. That causes TelemetryStopwatch to log an
+// error.
+SimpleTest.ignoreAllUncaughtExceptions(true);
+
+function waitFullscreenEvents(aDocument) {
+  return new Promise(resolve => {
+    function errorHandler() {
+      ok(false, "should not get fullscreenerror event");
+    }
+
+    let countFsChange = 0;
+    function changeHandler() {
+      ++countFsChange;
+      if (countFsChange == 2) {
+        aDocument.removeEventListener("fullscreenchange", changeHandler);
+        aDocument.removeEventListener("fullscreenerror", errorHandler);
+        resolve();
+      }
+    }
+
+    aDocument.addEventListener("fullscreenchange", changeHandler);
+    aDocument.addEventListener("fullscreenerror", errorHandler);
+  });
+}
+
+add_task(async function init() {
+  await pushPrefs(
+    ["full-screen-api.transition-duration.enter", "0 0"],
+    ["full-screen-api.transition-duration.leave", "0 0"]
+  );
+});
+
+add_task(async function navigation() {
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: `data:text/html,
+      <button id="button">Click here</button>
+      <script>
+        let button = document.getElementById("button");
+        button.addEventListener("click", function() {
+          button.requestFullscreen();
+          location.href = "about:blank";
+        });
+      </script>`,
+    },
+    async function(browser) {
+      let promiseFsEvents = waitFullscreenEvents(document);
+
+      await BrowserTestUtils.synthesizeMouseAtCenter("#button", {}, browser);
+      await promiseFsEvents;
+
+      ok(!window.fullScreen, "The chrome window should not be in fullscreen");
+      ok(
+        !document.documentElement.hasAttribute("inDOMFullscreen"),
+        "The chrome document should not be in fullscreen"
+      );
+    }
+  );
+});