Roll leveldb 3f7758:803d69 (v1.17 -> v1.18)
Upgrading from v1.17 to v1.18:
https://github.com/google/leveldb/releases/tag/v1.18
Note: This is the first release from the leveldb mirror of
https://github.com/google/leveldb. The prior 1.17 release was from
https://chromium.googlesource.com/external/leveldb.git/master which was a
mirror of the old Subversion repository at http://leveldb.googlecode.com/svn.
More information on this change at
https://code.google.com/p/chromium/issues/detail?id=415250.
BUG=429209
Review URL: https://codereview.chromium.org/
738553002
Cr-Commit-Position: refs/heads/master@{#304661}