Once the available
    loading units are generated and logged in
    <projectDirectory>/deferred_components_loading_units.yaml,
    it is possible to fully configure the pubspec’s
    deferred-components section so that the loading units
    are assigned to deferred components as desired.
    To continue with the box example, the generated
    deferred_components_loading_units.yaml file would contain:
    
loading-units:
  - id: 2
    libraries:
      - package:MyAppName/box.Dart
    

    The loading unit id (‘2’ in this case) is used
internally by Dart, and can be ignored.
The base loading unit (id ‘1’) is not listed
and contains everything not explicitly contained
in another loading unit.

    You can now add the following to pubspec.yaml: