Include statistics pointer in ImmutableDBOptions::Dump

Summary:
useful when debugging to tell whether a DB has stats enabled, and whether a stats object is shared across DBs.
Closes https://github.com/facebook/rocksdb/pull/2813

Differential Revision: D5741755

Pulled By: ajkr

fbshipit-source-id: 9b9d51dee77d14d415cd5da985d8d61b5b3837c3

options/db_options.cc

@@ -104,6 +104,8 @@ void ImmutableDBOptions::Dump(Logger* log) const {
                    info_log.get());
   ROCKS_LOG_HEADER(log, "               Options.max_file_opening_threads: %d",
                    max_file_opening_threads);
+  ROCKS_LOG_HEADER(log, "                             Options.statistics: %p",
+                   statistics.get());
   ROCKS_LOG_HEADER(log, "                              Options.use_fsync: %d",
                    use_fsync);
   ROCKS_LOG_HEADER(