WIP events: optimize emit()

[trevnorris]

EventEmitter#emit() can be called with many different arguments, but
there are a few that are most common. Increase performance by optimizing
those most common cases. It also drastically decreases the amount of
output from --trace_deopt.

This is a hyper optimization and will probably on save 100ns or so at actual runtime. One thing I find most advantageous is that --trace_deopt will show far less output.

There is still plenty that I would like to do. For example, implement a sort of IC in JS that will preempt what will be called. Would like feedback during development. Also one of the "message" tests is failing because of the change in the call stack. Will take care of that before WIP is removed.

R=@indutny

[indutny]

Is there any difference between throw new Error and throw Error.

[trevnorris]

Think the specification states that will always return a new Error object regardless. But since I'm there might as well switch it up to use new.

[indutny]

Mostly LGTM if it boosts performance or at least does not kill it ;)

[trevnorris]

@indutny Thanks. I'm going to sleep on it. There's still more to do. I would like to further implement an in JS IC that can preemptively call the correct emit function.

[dougwilson]

I feel like the function name should reflect that you should !this._events.error before calling. Perhaps $emitUncaughtError?

[trevnorris]

@dougwilson good point. thanks.

[charmander]

Is there a useful benchmark available?

[trevnorris]

Superseded by #601