Roll leveldb to r78 / 1.15.
changes that affect chrome:
- Fix for at least one cause of missing-files corruption: compaction errors now
immediately put the database into readonly mode instead of attempting
sophisticated recovery that was incompatible with Chromium's Env
implementation.
- Database will enter readonly mode when when a synchronous log write
succeeds but the sync fails.
BUG=239999
R=jsbell@chromium.org
Review URL: https://codereview.chromium.org/
111953003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239934 0039d316-1c4b-4281-b951-d872f2087c98