1 files changed, 26 insertions, 0 deletions
diff --git a/testing/web-platform/tests/longtask-timing/buffered-flag.window.js b/testing/web-platform/tests/longtask-timing/buffered-flag.window.js
new file mode 100644
index 0000000000..a0ba728ed2
--- /dev/null
+++ b/testing/web-platform/tests/longtask-timing/buffered-flag.window.js
@@ -0,0 +1,26 @@
+// META: script=resources/utils.js
+
+async_test(t => {
+    assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
+    new PerformanceObserver(t.step_func((entryList, obs) => {
+        const observer = new PerformanceObserver(t.step_func_done(list => {
+            let longtaskObserved = false;
+            list.getEntries().forEach(entry => {
+                if (entry.entryType === 'mark')
+                    return;
+                checkLongTaskEntry(entry);
+                longtaskObserved = true;
+            });
+            assert_true(longtaskObserved, 'Did not observe buffered longtask.');
+        }));
+        observer.observe({type: 'longtask', buffered: true});
+        // Observer mark so that we can flush the observer callback.
+        observer.observe({type: 'mark'});
+        performance.mark('m');
+        // Disconnect the embedding observer so this callback only runs once.
+        obs.disconnect();
+    })).observe({entryTypes: ['longtask']});
+    // Create a long task.
+    const begin = window.performance.now();
+    while (window.performance.now() < begin + 60);
+}, 'PerformanceObserver with buffered flag can see previous longtask entries.');