Unstable watched collections should trigger 'Model unstable' error

[pavelgj]

Right now they trigger Observer reaction functions should not change model.

[jbdeboer]

This was fixes, it seems.

iit('should throw assertion on unstable model', (RootScope rootScope, Logger log) {
          // Generates a different, equal, list on each evaluation.
          rootScope.context['list'] = new UnstableList();

          rootScope.watch('list.list', (n, v) => log(n));
          rootScope.digest();
        });

class UnstableList {
  List get list => new List.generate(3, (i) => i);
}

returns

Test failed: Caught Model did not stabilize in 5 digests. Last 3 iterations:
    list.list: [0, 1, 2] <= [0, 1, 2]
    list.list: [0, 1, 2] <= [0, 1, 2]
    list.list: [0, 1, 2] <= [0, 1, 2]

which looks like what we are expecting.

I'm not checking this test in since we already have similar ones.

[pavelgj]

No, here's the test case:

      iit('should throw "model unstable" error when observer is present', (RootScope rootScope, NgZone zone, ExceptionHandler e) {
        // Generates a different, equal, list on each evaluation.
        rootScope.context['list'] = new UnstableList();

        rootScope.watch('list.list', (n, v) => null, readOnly: true);
        try {
          zone.run(() => null);
        } catch(_) {}

        var errors = (e as LoggingExceptionHandler).errors;
        expect(errors.length).toEqual(1);
        expect(errors.first.error, startsWith('Model did not stabilize'));
      });

class UnstableList {
  List get list => new List.generate(3, (i) => i);
}