Currently connection assumes that transport is a websocket
and tries to handle websocket-related errors.
This patch:
- moves ConnectionTransport interface to use callbacks instead
of events. This way it could be used in browser context as well.
- introduces WebSocketTransport that implements ConnectionTransport
interface for ws.
This is a preparation step for 2 things:
- exposing `transport` option in the `puppeteer.connect` method
- better support for `browserify`
References #2119