I'm submitting a...

[x] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

NgZone throws a ReferenceError: Zone is not defined error when { ngZone: 'noop' } is used to bootstrap a module.

Expected behavior

Using the noop ngZone should not require Zone.js to be loaded.

I believe the regression was introduced here : #16863

We should probably have some kind of integration test for this.