Fixed missing std namespaces and make_unique.
Fixed missing std namespaces and make_unique.

cout/endl were missing the std namespace. Also std::make_unique
was used inadvertently which is part of C++14 and only C++11
is currently supported.

PiperOrigin-RevId: 243221310

dwing4g/leveldb,dwing4g/leveldb,google/leveldb,bitcoin-core/leveldb,cmumford/leveldb,likema/leveldb,bitcoin-core/leveldb,cmumford/leveldb,likema/leveldb,fastogt/leveldb,matehat/leveldb,bitcoin-core/leveldb,google/leveldb,dwing4g/leveldb,matehat/leveldb,matehat/leveldb,fastogt/leveldb