Assert boundary checks for SetPerfLevel()

Summary: Add asserts around PerfLevel enum

Test Plan: make all check -j32

Reviewers: sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D59007

util/perf_level.cc

@@ -4,9 +4,10 @@
 //  of patent rights can be found in the PATENTS file in the same directory.
 //
 
+#include <assert.h>
 #include <sstream>
-#include "util/perf_level_imp.h"
 #include "port/port.h"
+#include "util/perf_level_imp.h"
 
 namespace rocksdb {
 
@@ -17,6 +18,8 @@ __thread PerfLevel perf_level = kEnableCount;
 #endif
 
 void SetPerfLevel(PerfLevel level) {
+  assert(level > kUninitialized);
+  assert(level < kOutOfBounds);
   perf_level = level;
 }