* Enable prefer-const rule
Stylistically I don't like this but Closure Compiler takes advantage of
this information.
* Auto-fix lints
* Manually fix the remaining callsites
DevTools previously used the NPM events package for dispatching events. This package has an unfortunate flaw though- if a listener throws during event dispatch, no subsequent listeners are called. I've replaced that event dispatcher with my own implementation that ensures all listeners are called before it re-throws an error.
This commit replaces that event emitter with a custom implementation that calls all listeners before re-throwing an error.
