| <!DOCTYPE html> | |
| <script> | |
| function createPerformanceObserver(FunctionConstructor = Function) { | |
| const performanceObserver = new parent.PerformanceObserver(new FunctionConstructor(` | |
| this.callbackInvocations++; | |
| `)); | |
| performanceObserver.callbackInvocations = 0; | |
| performanceObserver.observe({ entryTypes: ["mark"] }); | |
| return performanceObserver; | |
| } | |
| </script> |