Add onWillThrowError

This will allow packages to override the dev tools popping up behavior.
`did-throw-error` emits only the message. This sucks. It should emit all the data available in the same form as `onWillThrowError`. we can either

* just change the param to the object, and suck up any breakages (metrics uses it) 
* Deprecate the `onDidThrowError` method, and suggest `onWillThrowError` instead

@nathansobo what do you think?