Client side measurement for Firefox, Chrome and Safari

[krausest]

I prepared a test runner that uses the idea of afterframe.js to measure the duration in the browser.
This will create less precise results for chrome, but it would allow comparing chrome with firefox and safari.
You can try it via npm run bench -- --runner webdriver-afterframe --browser firefox|safari|chrome
For some reason safari doesn't work with localhost. You have set the HOST variable to your ip address like HOST=192.168.178.86 npm run bench -- --runner webdriver-afterframe .... safaridriver and geckodriver must be installed manually to run the tests.

I performed a run some time ago, but it needs some work for which I don't find the time:

• Check the results. Considering the complexity getting the right duration for all the frameworks (like timers, rafs) I can't imagine afterframe.js gets them right. After that either the measurement should be improved otherwise some frameworks must be excluded.
• Develop an idea what comparison is most interesting. Relative duration across the browsers for one implementation?

See also #1254