Private list property is empty when hot restart the app when using with keyword.

**Steps to Reproduce**
My class is like below.
```dart
class A with B, C, D { }
```
When i use private list properties in class B, hive works fine and put data to the box but when I hot restart the app hive gives me empty list.

For example I changed _listProperty to listProperty, hive worked right.

**Version**
- Platform: iOS, Android, Mac, Windows, Linux, Web
- Flutter version: 1.1.0
- Hive version: 2.1.0

Start by reproducing the hot-restart behavior with class A using mixins B, C, and D, and a private list property in B. Check whether data written to the Hive box is restored after restart; done means the private list is no longer empty, with a regression test covering this example.

Written by the indexing model from the issue text.