setGlobalHandler(fun) {
    _globalHandler = fun;
  }
The particular require runtime that we are using looks for a global
`ErrorUtils` object and if it exists, then it requires modules with the
error handler specified via ErrorUtils.setGlobalHandler by calling the
require function with applyWithGuard. Since the require module is loaded
before any of the modules, this ErrorUtils must be defined (and the handler
set) globally before requiring anything.