test(dccd): add map reference reassignment test

Author: rkirov

test/change_detection/dirty_checking_change_detector_spec.dart

@@ -977,7 +977,7 @@ void addListSpec({bool useObservable}) {
           removals: []));
     }));
 
-    iit('should list reference changes', () {
+    it('should handle list reference changes', () {
       var list = listFactory(['a']);
       var record = detector.watch(list, null, null);
       if (detector.collectChanges().moveNext()) {
@@ -1140,6 +1140,23 @@ void addMapSpec({bool useObservable}) {
 
       expect(getChangeIterator().moveNext()).toEqual(false);
     }));
+
+    iit('should handle map reference changes', wrap(() {
+      var map = mapFactory({'foo': 'bar'});
+      var record = detector.watch(map, null, 'handler');
+
+      expect(getChangeIterator().moveNext()).toEqual(true);
+
+      record.object = mapFactory({'bar': 'buz'});
+      var iterator = getChangeIterator();
+      expect(iterator.moveNext()).toEqual(true);
+      expect(iterator.current.currentValue, toEqualMapRecord(
+          map: [],
+          previous: ['a[A -> null]', 'd[D -> null]'],
+          additions: ['bar[null -> buz]'],
+          changes: [],
+          removals: ['foo[bar -> null]']));
+    }));
   });
 }