This patch introduces a page.waitForFileChooser() method
that adds a watchdog to wait for file chooser dialogs.
This lets Puppeteer users to capture file chooser requests
and fulfill/cancel them if necessary.
Fixes#2946
Certain Puppeteer methods do expose the inner browser - e.g.
`browser.version()` depends on the browser we run.
Split out these tests into a vendor-specific test suites.
References #3889