`RewindBlockIndex` was made to allow nodes upgrading to new consensus rules post-segwit fork to 
download new consensus data (i.e witnesses) without having to go through a whole IBD. It has been pointed than now really few pre-segwit nodes care to upgrade and that this logic may be irrelevant.

See https://github.com/bitcoin/bitcoin/pull/17737#discussion_r358514335 in review  of #17737 for more context pointers.
public:
    
    
    CCoinsViewDB m_dbview GUARDED_BY(cs_main);
    
    CCoinsViewErrorCatcher m_catcherview GUARDED_BY(cs_main);
    
    
    std::unique_ptr<CCoinsViewCache> m_cacheview GUARDED_BY(cs_main);
    
    
    
    
    
    
    CoinsViews(std::string ldb_name, size_t cache_size_bytes, bool in_memory, bool should_wipe);
    
    void InitCache() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
};
enum class CoinsCacheSizeState