DEPS.xwalk: Roll v8-crosswalk (64b8b78 -> b85d25a).

b85d25a Merge pull request #36 from huningxin/crosswalk-6/35.0.1916.114
6433f03 Fixed a typo: psrlq -> psrldq.
Merge pull request #2039 from rakuco/v6-roll-v8

DEPS.xwalk: Roll v8-crosswalk (64b8b78 -> b85d25a).