Add --index_block_restart_interval option in db_bench

Summary:
Pass --index_block_restart_interval flag to block_based_options in db_bench tool.

Test Plan: none

Reviewers: sdong, kradhakrishnan

Reviewed By: kradhakrishnan

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57699

tools/db_bench_tool.cc

@@ -350,7 +350,12 @@ DEFINE_int32(block_size,
 DEFINE_int32(block_restart_interval,
              rocksdb::BlockBasedTableOptions().block_restart_interval,
              "Number of keys between restart points "
-             "for delta encoding of keys.");
+             "for delta encoding of keys in data block.");
+
+DEFINE_int32(index_block_restart_interval,
+             rocksdb::BlockBasedTableOptions().index_block_restart_interval,
+             "Number of keys between restart points "
+             "for delta encoding of keys in index block.");
 
 DEFINE_int64(compressed_cache_size, -1,
              "Number of bytes to use as a cache of compressed data.");
@@ -2541,6 +2546,8 @@ class Benchmark {
       block_based_options.block_cache_compressed = compressed_cache_;
       block_based_options.block_size = FLAGS_block_size;
       block_based_options.block_restart_interval = FLAGS_block_restart_interval;
+      block_based_options.index_block_restart_interval =
+          FLAGS_index_block_restart_interval;
       block_based_options.filter_policy = filter_policy_;
       block_based_options.skip_table_builder_flush =
           FLAGS_skip_table_builder_flush;