Crashed plugins don't (necessarily) crash the wrapper

[davidben]

Older generations of browsers would run plugins in-process, so the wrapper would try to avoid crashing when the viewer did, as a nasty hack. Nowadays this logic is unnecessary as modern browsers run plugins in separate processes. In fact the logic is harmful as it gets in the way of the browser's own crash logic and instead just returns an error to all queries.

We should drop this logic and just crash the browser. Unfortunately, there still exist random niche browsers which run plugins in-process and they still need the hack. We can sniff the user agent, but It may be worth talking to the NPAPI development list and seeing if we can get a safe "I've crashed, kill me now" hook for modern browsers to implement.