Simplified RepeatedPtrField to vector conversion.
Simplified RepeatedPtrField to vector conversion.

It's also possible that `vector` can take advantage of
`RepeatedPtrField` iterators implementing `RandomAccessIterator`
concept and avoid buffer resizes, when constructed from range.

Review: https://reviews.apache.org/r/62973/

gsantovena/mesos,asamerh4/mesos,dforsyth/mesos,zmalik/mesos,kaysoky/mesos,asamerh4/mesos,abudnik/mesos,andschwa/mesos,zmalik/mesos,kaysoky/mesos,dforsyth/mesos,gsantovena/mesos,Gilbert88/mesos,Gilbert88/mesos,zmalik/mesos,chhsia0/mesos,kaysoky/mesos,Gilbert88/mesos,Gilbert88/mesos,Gilbert88/mesos,dforsyth/mesos,andschwa/mesos,jpeach/mesos,jpeach/mesos,jpeach/mesos,kaysoky/mesos,reneploetz/mesos,asamerh4/mesos,chhsia0/mesos,andschwa/mesos,gsantovena/mesos,reneploetz/mesos,abudnik/mesos,asamerh4/mesos,jpeach/mesos,reneploetz/mesos,jpeach/mesos,andschwa/mesos,zmalik/mesos,andschwa/mesos,abudnik/mesos,dforsyth/mesos,zmalik/mesos,chhsia0/mesos,asamerh4/mesos,gsantovena/mesos,Gilbert88/mesos,abudnik/mesos,andschwa/mesos,dforsyth/mesos,jpeach/mesos,zmalik/mesos,gsantovena/mesos,kaysoky/mesos,chhsia0/mesos,zmalik/mesos,abudnik/mesos,dforsyth/mesos,asamerh4/mesos,asamerh4/mesos,abudnik/mesos,Gilbert88/mesos,andschwa/mesos,chhsia0/mesos,abudnik/mesos,chhsia0/mesos,kaysoky/mesos,jpeach/mesos,reneploetz/mesos,gsantovena/mesos,reneploetz/mesos,dforsyth/mesos,gsantovena/mesos,chhsia0/mesos,reneploetz/mesos,reneploetz/mesos,kaysoky/mesos