Fix compile error when NROCKSDB_THREAD_STATUS is not used.

Summary: Fix compile error when NROCKSDB_THREAD_STATUS is not used.

Test Plan: make dbg OPT=-DNROCKSDB_THREAD_STATUS -j32

Reviewers: sdong, igor, rven

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D35847

util/thread_status_impl.cc

@@ -70,8 +70,8 @@ const std::string& ThreadStatus::GetStateName(
   return dummy_str;
 }
 
-const std::string ThreadStatus::TimeToString(
-    int64_t time) {
+const std::string ThreadStatus::MicrosToString(
+    uint64_t op_elapsed_time) {
   static std::string dummy_str = "";
   return dummy_str;
 }