1 files changed, 66 insertions, 0 deletions
diff --git a/testing/web-platform/tests/performance-timeline/po-callback-mutate.any.js b/testing/web-platform/tests/performance-timeline/po-callback-mutate.any.js
new file mode 100644
index 0000000000..8f1b09bc37
--- /dev/null
+++ b/testing/web-platform/tests/performance-timeline/po-callback-mutate.any.js
@@ -0,0 +1,66 @@
+// META: script=performanceobservers.js
+
+  async_test(function (t) {
+    var callbackCount = 0;
+    var observer = new PerformanceObserver(
+        t.step_func(function (entryList, obs) {
+          callbackCount++;
+
+          if (callbackCount === 1) {
+            checkEntries(entryList.getEntries(), [
+              {entryType: "measure", name: "measure1"},
+            ]);
+            observer.observe({entryTypes: ["mark"]});
+            self.performance.mark("mark2");
+            self.performance.measure("measure2");
+            return;
+          }
+
+          if (callbackCount === 2) {
+            checkEntries(entryList.getEntries(), [
+              {entryType: "mark", name: "mark2"},
+            ]);
+            self.performance.mark("mark-before-change-observe-state-to-measure");
+            self.performance.measure("measure-before-change-observe-state-to-measure");
+            observer.observe({entryTypes: ["measure"]});
+            self.performance.mark("mark3");
+            self.performance.measure("measure3");
+            return;
+          }
+
+          if (callbackCount === 3) {
+            checkEntries(entryList.getEntries(), [
+              {entryType: "measure", name: "measure3"},
+              {entryType: "mark", name: "mark-before-change-observe-state-to-measure"},
+            ]);
+            self.performance.mark("mark-before-change-observe-state-to-both");
+            self.performance.measure("measure-before-change-observe-state-to-both");
+            observer.observe({entryTypes: ["mark", "measure"]});
+            self.performance.mark("mark4");
+            self.performance.measure("measure4");
+            return;
+          }
+
+          if (callbackCount === 4) {
+            checkEntries(entryList.getEntries(), [
+              {entryType: "measure", name: "measure-before-change-observe-state-to-both"},
+              {entryType: "measure", name: "measure4"},
+              {entryType: "mark", name: "mark4"},
+            ]);
+            self.performance.mark("mark-before-disconnect");
+            self.performance.measure("measure-before-disconnect");
+            observer.disconnect();
+            self.performance.mark("mark-after-disconnect");
+            self.performance.measure("measure-after-disconnect");
+            t.done();
+            return;
+          }
+
+          assert_unreached("The callback must not be invoked after disconnecting");
+        })
+      );
+
+    observer.observe({entryTypes: ["measure"]});
+    self.performance.mark("mark1");
+    self.performance.measure("measure1");
+  }, "PerformanceObserver modifications inside callback should update filtering and not clear buffer");