[split] [util-core] special case buf.slice(0, buf.length)
[split] [util-core] special case buf.slice(0, buf.length)

Problem

buf.slice can be called with i = 0 and j >= length. This causes an
unnecessary copy to be made.

Solution

Special cases this to return the same buf.

Result

slice() can be called without having to check for this case or worry
about unnecessary allocations.

RB_ID=336549

folone/util,travisbrown/util,slackhappy/util,cogitate/twitter-util-uuid,tenghuihua/util,hydro2k/util,luciferous/util,twitter/util,wuqiangxjtu/util,nkhuyu/util,slackhappy/util,stremlenye/util,wuqiangxjtu/util,wuqiangxjtu/util,tenghuihua/util,nkhuyu/util,luciferous/util,tdyas/util,twitter/util,travisbrown/util,RUNDSP/util,BuoyantIO/twitter-util,edombowsky/util,Jiri-Kremser/util,BuoyantIO/twitter-util,LitmusHealth/twitter-utils,RUNDSP/util,edombowsky/util,wuqiangxjtu/util,RUNDSP/util,BuoyantIO/twitter-util,edombowsky/util,cogitate/twitter-util-uuid,LitmusHealth/twitter-utils,hydro2k/util,LitmusHealth/twitter-utils,nkhuyu/util,tdyas/util,Jiri-Kremser/util,luciferous/util,folone/util,slackhappy/util,Jiri-Kremser/util,LitmusHealth/twitter-utils,travisbrown/util,twitter/util,cogitate/twitter-util-uuid,tenghuihua/util,RUNDSP/util,luciferous/util,tdyas/util,travisbrown/util,tenghuihua/util,cogitate/twitter-util-uuid,stremlenye/util,nkhuyu/util,edombowsky/util,BuoyantIO/twitter-util,stremlenye/util,hydro2k/util,stremlenye/util,folone/util,folone/util,hydro2k/util,slackhappy/util,Jiri-Kremser/util,tdyas/util