Make Rollback fields private and add accessors.

This changes the Rollback class to make its fields private.
Getters and setters are added as needed to access these fields.

This is a prelude to adding synchronisation to the Rollback class.

Bug: 136241838
Test: atest RollbackTest
Test: new unit test added RollbackUnitTest
Change-Id: I223b82094287b11980d90e530525a9696258471b
4 files changed