make ExampleExecAllocatorOption less flaky
make ExampleExecAllocatorOption less flaky

The Default folder is created asynchronously to Chrome starting to
listen on the debugging protocol port. So we can't expect it to exist.

Instead, base the example on DevToolsActivePort, which we can rely on.

chromedp/chromedp,knq/chromedp,chromedp/chromedp,knq/chromedp,knq/chromedp,chromedp/chromedp