Reorder the member variables of FileMetaData to improve cache locality.
Reorder the member variables of FileMetaData to improve cache locality.

Summary:
Move stats related member variables of FileMetaData to the bottom to
improve cache locality of normal DB operations.

Test Plan: make

Reviewers: haobo, ljin, sdong

Reviewed By: sdong

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19287

wenduo/rocksdb,IMCG/RcoksDB,anagav/rocksdb,alihalabyah/rocksdb,wlqGit/rocksdb,skunkwerks/rocksdb,lgscofield/rocksdb,flabby/rocksdb,wat-ze-hex/rocksdb,tizzybec/rocksdb,Andymic/rocksdb,biddyweb/rocksdb,skunkwerks/rocksdb,IMCG/RcoksDB,biddyweb/rocksdb,RyanTech/rocksdb,hobinyoon/rocksdb,tschottdorf/rocksdb,siddhartharay007/rocksdb,tizzybec/rocksdb,tsheasha/rocksdb,dkorolev/rocksdb,vashstorm/rocksdb,OverlordQ/rocksdb,luckywhu/rocksdb,rDSN-Projects/rocksdb.replicated,tsheasha/rocksdb,JackLian/rocksdb,vmx/rocksdb,JackLian/rocksdb,RyanTech/rocksdb,lgscofield/rocksdb,lgscofield/rocksdb,ryneli/rocksdb,facebook/rocksdb,lgscofield/rocksdb,zhangpng/rocksdb,Vaisman/rocksdb,zhangpng/rocksdb,Vaisman/rocksdb,wat-ze-hex/rocksdb,kaschaeffer/rocksdb,Andymic/rocksdb,makelivedotnet/rocksdb,NickCis/rocksdb,makelivedotnet/rocksdb,facebook/rocksdb,flabby/rocksdb,temicai/rocksdb,zhangpng/rocksdb,flabby/rocksdb,flabby/rocksdb,makelivedotnet/rocksdb,biddyweb/rocksdb,bbiao/rocksdb,JoeWoo/rocksdb,lgscofield/rocksdb,NickCis/rocksdb,tschottdorf/rocksdb,sorphi/rocksdb,alihalabyah/rocksdb,jalexanderqed/rocksdb,Applied-Duality/rocksdb,caijieming-baidu/rocksdb,ylong/rocksdb,bbiao/rocksdb,ryneli/rocksdb,alihalabyah/rocksdb,mbarbon/rocksdb,geraldoandradee/rocksdb,caijieming-baidu/rocksdb,temicai/rocksdb,facebook/rocksdb,NickCis/rocksdb,luckywhu/rocksdb,vmx/rocksdb,wlqGit/rocksdb,virtdb/rocksdb,tschottdorf/rocksdb,fengshao0907/rocksdb,JohnPJenkins/rocksdb,JohnPJenkins/rocksdb,flabby/rocksdb,tizzybec/rocksdb,kaschaeffer/rocksdb,wat-ze-hex/rocksdb,lgscofield/rocksdb,wenduo/rocksdb,tizzybec/rocksdb,norton/rocksdb,ylong/rocksdb,OverlordQ/rocksdb,alihalabyah/rocksdb,skunkwerks/rocksdb,vashstorm/rocksdb,geraldoandradee/rocksdb,siddhartharay007/rocksdb,JoeWoo/rocksdb,Andymic/rocksdb,zhangpng/rocksdb,sorphi/rocksdb,jalexanderqed/rocksdb,SunguckLee/RocksDB,norton/rocksdb,skunkwerks/rocksdb,dkorolev/rocksdb,kaschaeffer/rocksdb,tsheasha/rocksdb,NickCis/rocksdb,JackLian/rocksdb,zhangpng/rocksdb,msb-at-yahoo/rocksdb,vashstorm/rocksdb,anagav/rocksdb,wenduo/rocksdb,norton/rocksdb,geraldoandradee/rocksdb,RyanTech/rocksdb,OverlordQ/rocksdb,virtdb/rocksdb,skunkwerks/rocksdb,OverlordQ/rocksdb,tizzybec/rocksdb,luckywhu/rocksdb,Vaisman/rocksdb,Andymic/rocksdb,kaschaeffer/rocksdb,siddhartharay007/rocksdb,JohnPJenkins/rocksdb,Vaisman/rocksdb,RyanTech/rocksdb,kaschaeffer/rocksdb,tschottdorf/rocksdb,tsheasha/rocksdb,caijieming-baidu/rocksdb,mbarbon/rocksdb,norton/rocksdb,ryneli/rocksdb,makelivedotnet/rocksdb,ylong/rocksdb,rDSN-Projects/rocksdb.replicated,luckywhu/rocksdb,IMCG/RcoksDB,caijieming-baidu/rocksdb,hobinyoon/rocksdb,sorphi/rocksdb,ylong/rocksdb,geraldoandradee/rocksdb,caijieming-baidu/rocksdb,mbarbon/rocksdb,siddhartharay007/rocksdb,biddyweb/rocksdb,SunguckLee/RocksDB,geraldoandradee/rocksdb,Andymic/rocksdb,bbiao/rocksdb,wlqGit/rocksdb,makelivedotnet/rocksdb,facebook/rocksdb,dkorolev/rocksdb,wlqGit/rocksdb,siddhartharay007/rocksdb,fengshao0907/rocksdb,ryneli/rocksdb,biddyweb/rocksdb,mbarbon/rocksdb,ylong/rocksdb,biddyweb/rocksdb,wlqGit/rocksdb,hobinyoon/rocksdb,sorphi/rocksdb,sorphi/rocksdb,luckywhu/rocksdb,rDSN-Projects/rocksdb.replicated,amyvmiwei/rocksdb,vashstorm/rocksdb,hobinyoon/rocksdb,zhangpng/rocksdb,JackLian/rocksdb,alihalabyah/rocksdb,wskplho/rocksdb,wskplho/rocksdb,RyanTech/rocksdb,sorphi/rocksdb,JohnPJenkins/rocksdb,flabby/rocksdb,anagav/rocksdb,norton/rocksdb,wskplho/rocksdb,wskplho/rocksdb,bbiao/rocksdb,JohnPJenkins/rocksdb,ryneli/rocksdb,bbiao/rocksdb,ylong/rocksdb,anagav/rocksdb,ryneli/rocksdb,vashstorm/rocksdb,hobinyoon/rocksdb,kaschaeffer/rocksdb,wenduo/rocksdb,temicai/rocksdb,amyvmiwei/rocksdb,wat-ze-hex/rocksdb,IMCG/RcoksDB,virtdb/rocksdb,temicai/rocksdb,anagav/rocksdb,tizzybec/rocksdb,fengshao0907/rocksdb,norton/rocksdb,luckywhu/rocksdb,OverlordQ/rocksdb,tsheasha/rocksdb,jalexanderqed/rocksdb,msb-at-yahoo/rocksdb,virtdb/rocksdb,norton/rocksdb,JoeWoo/rocksdb,mbarbon/rocksdb,wlqGit/rocksdb,norton/rocksdb,alihalabyah/rocksdb,Applied-Duality/rocksdb,kaschaeffer/rocksdb,tschottdorf/rocksdb,temicai/rocksdb,IMCG/RcoksDB,tsheasha/rocksdb,skunkwerks/rocksdb,wat-ze-hex/rocksdb,Applied-Duality/rocksdb,RyanTech/rocksdb,Applied-Duality/rocksdb,ylong/rocksdb,Applied-Duality/rocksdb,JohnPJenkins/rocksdb,JackLian/rocksdb,wenduo/rocksdb,geraldoandradee/rocksdb,vashstorm/rocksdb,Applied-Duality/rocksdb,JohnPJenkins/rocksdb,IMCG/RcoksDB,amyvmiwei/rocksdb,rDSN-Projects/rocksdb.replicated,jalexanderqed/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,Andymic/rocksdb,msb-at-yahoo/rocksdb,virtdb/rocksdb,lgscofield/rocksdb,RyanTech/rocksdb,ryneli/rocksdb,vmx/rocksdb,mbarbon/rocksdb,hobinyoon/rocksdb,siddhartharay007/rocksdb,caijieming-baidu/rocksdb,amyvmiwei/rocksdb,biddyweb/rocksdb,jalexanderqed/rocksdb,SunguckLee/RocksDB,msb-at-yahoo/rocksdb,hobinyoon/rocksdb,fengshao0907/rocksdb,alihalabyah/rocksdb,makelivedotnet/rocksdb,wenduo/rocksdb,tschottdorf/rocksdb,hobinyoon/rocksdb,sorphi/rocksdb,wskplho/rocksdb,vashstorm/rocksdb,JoeWoo/rocksdb,facebook/rocksdb,JoeWoo/rocksdb,bbiao/rocksdb,jalexanderqed/rocksdb,wenduo/rocksdb,luckywhu/rocksdb,Vaisman/rocksdb,geraldoandradee/rocksdb,skunkwerks/rocksdb,JackLian/rocksdb,makelivedotnet/rocksdb,OverlordQ/rocksdb,SunguckLee/RocksDB,Vaisman/rocksdb,temicai/rocksdb,virtdb/rocksdb,NickCis/rocksdb,dkorolev/rocksdb,vmx/rocksdb,temicai/rocksdb,facebook/rocksdb,rDSN-Projects/rocksdb.replicated,caijieming-baidu/rocksdb,facebook/rocksdb,wskplho/rocksdb,JoeWoo/rocksdb,tsheasha/rocksdb,NickCis/rocksdb,Vaisman/rocksdb,anagav/rocksdb,Andymic/rocksdb,fengshao0907/rocksdb,Andymic/rocksdb,vmx/rocksdb,fengshao0907/rocksdb,amyvmiwei/rocksdb,SunguckLee/RocksDB,fengshao0907/rocksdb,dkorolev/rocksdb,wskplho/rocksdb,amyvmiwei/rocksdb,SunguckLee/RocksDB,facebook/rocksdb,wat-ze-hex/rocksdb,anagav/rocksdb,flabby/rocksdb,SunguckLee/RocksDB,virtdb/rocksdb,wlqGit/rocksdb,SunguckLee/RocksDB,vmx/rocksdb,NickCis/rocksdb,wenduo/rocksdb,wat-ze-hex/rocksdb,rDSN-Projects/rocksdb.replicated,amyvmiwei/rocksdb,tsheasha/rocksdb,jalexanderqed/rocksdb,vmx/rocksdb,Applied-Duality/rocksdb,vmx/rocksdb,dkorolev/rocksdb,tizzybec/rocksdb,bbiao/rocksdb,IMCG/RcoksDB,msb-at-yahoo/rocksdb,zhangpng/rocksdb,JackLian/rocksdb,JoeWoo/rocksdb,mbarbon/rocksdb,siddhartharay007/rocksdb,rDSN-Projects/rocksdb.replicated,OverlordQ/rocksdb,dkorolev/rocksdb,msb-at-yahoo/rocksdb