Add plugin hook for createBrowser

[sjelin]

People want to modify the capabilities of a browser before it is created. Seems like a legitimate use case to me. We should add a plugin hook at the top of Runner#createBrowser().

[NickTomlin]

👍

Do we have a diagram or documentation on all the hooks/possible transformations? I feel like it would be awesome to review the current state and then come up with an "ideal" state of lifecycle methods we could expose.

[seanmay]

I feel like this is the appropriate short-term solution.

It might cause future headaches, in terms of plugins monkey-patching content, especially if we ever look at separating the direct Selenium WebDriver bindings from that object (something I'm working on initial steps for, by turning it into a façade that proxies calls, rather than a subclass). But this shouldn't hurt too many people, and if they're taking this tack, it seems like either they aren't going to be using TS types, or they don't care about any leaking into their tests, anyway.