Add db_bench flag to set cache_index_and_filter_blocks

Summary:
The new flag --cache_index_and_filter_blocks sets
BlockBasedTableOptions.cache_index_and_filter_blocks

Test Plan: make db_bench. Working on benchmarks with the new flag.

Reviewers: igor

Reviewed By: igor

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D41481

db/db_bench.cc

@@ -310,6 +310,9 @@ DEFINE_int32(universal_compression_size_percent, -1,
 DEFINE_int64(cache_size, -1, "Number of bytes to use as a cache of uncompressed"
              "data. Negative means use default settings.");
 
+DEFINE_bool(cache_index_and_filter_blocks, false,
+            "Cache index/filter blocks in block cache.");
+
 DEFINE_int32(block_size,
              static_cast<int32_t>(rocksdb::BlockBasedTableOptions().block_size),
              "Number of bytes in a block.");
@@ -2371,6 +2374,8 @@ class Benchmark {
       if (cache_ == nullptr) {
         block_based_options.no_block_cache = true;
       }
+      block_based_options.cache_index_and_filter_blocks =
+          FLAGS_cache_index_and_filter_blocks;
       block_based_options.block_cache = cache_;
       block_based_options.block_cache_compressed = compressed_cache_;
       block_based_options.block_size = FLAGS_block_size;