test: fix flaky test (#2650)
test: fix flaky test (#2650)

When launching browser with a default URL, the page is not necessarily
loaded when we're reaching into it.
puppeteer/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer,puppeteer/puppeteer,puppeteer/puppeteer,GoogleChrome/puppeteer