[Performance Branch] PlainTable to encode rows with seqID 0, value type using 1 internal byte.

Summary: In PlainTable, use one single byte to represent 8 bytes of internal bytes, if seqID = 0 and it is value type (which should be common for bottom most files). It is to save 7 bytes for uncompressed cases.

Test Plan: make all check

Reviewers: haobo, dhruba, kailiu

Reviewed By: haobo

CC: igor, leveldb

Differential Revision: https://reviews.facebook.net/D15489

table/block_builder.cc

@@ -36,6 +36,7 @@
 #include <algorithm>
 #include <assert.h>
 #include "rocksdb/comparator.h"
+#include "db/dbformat.h"
 #include "util/coding.h"
 
 namespace rocksdb {
@@ -51,9 +52,8 @@ BlockBuilder::BlockBuilder(int block_restart_interval,
   restarts_.push_back(0);       // First restart point is at offset 0
 }
 
-BlockBuilder::BlockBuilder(const Options& options)
-    : BlockBuilder(options.block_restart_interval, options.comparator) {
-}
+BlockBuilder::BlockBuilder(const Options& options, const Comparator* comparator)
+    : BlockBuilder(options.block_restart_interval, comparator) {}
 
 void BlockBuilder::Reset() {
   buffer_.clear();