1 files changed, 16 insertions, 0 deletions
diff --git a/testing/web-platform/tests/longtask-timing/longtask-before-observer.window.js b/testing/web-platform/tests/longtask-timing/longtask-before-observer.window.js
new file mode 100644
index 0000000000..79d6990cf8
--- /dev/null
+++ b/testing/web-platform/tests/longtask-timing/longtask-before-observer.window.js
@@ -0,0 +1,16 @@
+// META: script=resources/utils.js
+
+async_test(t => {
+  assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
+  // Create a long task before any observer.
+  const begin = window.performance.now();
+  while (window.performance.now() < begin + 60);
+  // After a timeout, add an observer with buffered flag.
+  t.step_timeout(() => {
+    new PerformanceObserver(t.step_func_done(list => {
+      list.getEntries().forEach(entry => {
+        checkLongTaskEntry(entry);
+      });
+    })).observe({type: 'longtask', buffered: true});
+  }, 0);
+}, 'PerformanceObserver with buffered flag can see previous longtask entries.');