This patch:
- adds `worker.evaluate` and `worker.evaluateHandle` methods as a shortcut to their execution context equivalents.
- makes the error messages a bit nicer when interacting with a closed worker (as opposed to a closed page).
- moves the worker tests into their own spec file.
Some of the worker tests were failing on the bots. After investigating, I found one race in the test, and one race upstream in Chromium which I filed upstream as https://crbug.com/846099. But I added a small hack here as a temporary workaround.
References #2632
This adds `page.workers()`, and two events `workercreated` and `workerdestroyed`. It also forwards logs from a worker into the page `console` event.
Only dedicated workers are supported for now, ServiceWorkers will probably work differently because they aren't necessarily associated with a single page.
Fixes#2350.
