Removed the implicit and value changing conversion in log benchmark.
Removed the implicit and value changing conversion in log benchmark.

Whether `char` is signed or not is up to the implementation, so be more
explicit here. Also, since we want a `char` with all bits set, use a
value representation that more clearly communicates that.

Review: https://reviews.apache.org/r/43240/

chhsia0/mesos,neilconway/mesos,jpeach/mesos,Gilbert88/mesos,dforsyth/mesos,gsantovena/mesos,chhsia0/mesos,gsantovena/mesos,asamerh4/mesos,Aman-Jain-14/customizedMesos,kaysoky/mesos,neilconway/mesos,jpeach/mesos,asamerh4/mesos,asamerh4/mesos,neilconway/mesos,jpeach/mesos,andschwa/mesos,yuquanshan/customizedMesos,neilconway/mesos,gsantovena/mesos,dforsyth/mesos,verizonlabs/mesos,verizonlabs/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,jpeach/mesos,Gilbert88/mesos,zmalik/mesos,gsantovena/mesos,dforsyth/mesos,jpeach/mesos,asamerh4/mesos,reneploetz/mesos,chhsia0/mesos,Aman-Jain-14/customizedMesos,yuquanshan/customizedMesos,abudnik/mesos,abudnik/mesos,jpeach/mesos,neilconway/mesos,yuquanshan/customizedMesos,verizonlabs/mesos,yuquanshan/customizedMesos,andschwa/mesos,reneploetz/mesos,Gilbert88/mesos,craimbert/mesos,jpeach/mesos,reneploetz/mesos,verizonlabs/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,asamerh4/mesos,Gilbert88/mesos,kaysoky/mesos,andschwa/mesos,Gilbert88/mesos,craimbert/mesos,gsantovena/mesos,zmalik/mesos,kaysoky/mesos,neilconway/mesos,kaysoky/mesos,gsantovena/mesos,dforsyth/mesos,abudnik/mesos,reneploetz/mesos,kaysoky/mesos,verizonlabs/mesos,abudnik/mesos,andschwa/mesos,chhsia0/mesos,dforsyth/mesos,asamerh4/mesos,chhsia0/mesos,kaysoky/mesos,abudnik/mesos,andschwa/mesos,kaysoky/mesos,zmalik/mesos,Aman-Jain-14/customizedMesos,zmalik/mesos,asamerh4/mesos,yuquanshan/customizedMesos,zmalik/mesos,reneploetz/mesos,craimbert/mesos,craimbert/mesos,reneploetz/mesos,andschwa/mesos,craimbert/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,neilconway/mesos,Gilbert88/mesos,andschwa/mesos,craimbert/mesos,chhsia0/mesos,reneploetz/mesos,yuquanshan/customizedMesos,abudnik/mesos,zmalik/mesos,chhsia0/mesos,verizonlabs/mesos,abudnik/mesos,dforsyth/mesos,craimbert/mesos,Aman-Jain-14/customizedMesos,verizonlabs/mesos,zmalik/mesos,gsantovena/mesos