1 files changed, 36 insertions, 0 deletions
diff --git a/testing/web-platform/tests/paint-timing/with-first-paint/buffered-flag.window.js b/testing/web-platform/tests/paint-timing/with-first-paint/buffered-flag.window.js
new file mode 100644
index 0000000000..0b7c8bea2e
--- /dev/null
+++ b/testing/web-platform/tests/paint-timing/with-first-paint/buffered-flag.window.js
@@ -0,0 +1,36 @@
+setup({"hide_test_state": true});
+async_test(t => {
+  assert_implements(window.PerformancePaintTiming, "Paint Timing isn't supported.");
+  // First observer creates second in callback to ensure the entry has been dispatched by the time
+  // the second observer begins observing.
+  let entries_seen = 0;
+  new PerformanceObserver(firstList => {
+    entries_seen += firstList.getEntries().length;
+    // Abort if we have not yet received both paint entries.
+    if (entries_seen < 2)
+      return;
+
+    // Second observer requires 'buffered: true' to see the entries.
+    let firstPaintSeen = false;
+    let firstContentfulPaintSeen = false;
+    new PerformanceObserver(list => {
+      list.getEntries().forEach(t.step_func(entry => {
+        assert_equals(entry.entryType, 'paint');
+        if (entry.name === 'first-paint')
+          firstPaintSeen = true;
+        else if (entry.name === 'first-contentful-paint')
+          firstContentfulPaintSeen = true;
+        else
+          assert_unreached('The observer should only see first paint or first contentful paint!');
+
+        if (firstPaintSeen && firstContentfulPaintSeen)
+          t.done();
+      }));
+    }).observe({'type': 'paint', buffered: true});
+  }).observe({'entryTypes': ['paint']});
+
+  // Trigger the first paint entries
+  const img = document.createElement("IMG");
+  img.src = "resources/circles.png";
+  document.body.appendChild(img);
+}, "PerformanceObserver with buffered flag sees previous paint entries.");