stackable_db: add default function for GetLiveFilesMetaData()

Summary: stackable_db doesn't have GetLiveFilesMetaData() implemented. Add it

Test Plan: make all check

Reviewers: yhchiang, ljin, igor

Reviewed By: igor

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19491

include/utilities/stackable_db.h

@@ -171,6 +171,11 @@ class StackableDB : public DB {
     return db_->EnableFileDeletions(force);
   }
 
+  virtual void GetLiveFilesMetaData(
+      std::vector<LiveFileMetaData>* metadata) override {
+    db_->GetLiveFilesMetaData(metadata);
+  }
+
   virtual Status GetLiveFiles(std::vector<std::string>& vec, uint64_t* mfs,
                               bool flush_memtable = true) override {
       return db_->GetLiveFiles(vec, mfs, flush_memtable);