Factor out datasource stats function.
Factor out datasource stats function.

tilemill-project/tilemill,paulovieira/tilemill-clima,tizzybec/tilemill,Zhao-Qi/tilemill,tizzybec/tilemill,tilemill-project/tilemill,Zhao-Qi/tilemill,isaacs/tilemill,paulovieira/tilemill-clima,isaacs/tilemill,fxtentacle/tilemill,mbrukman/tilemill,Zhao-Qi/tilemill,mbrukman/tilemill,mbrukman/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,paulovieira/tilemill-clima,MappingKat/tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,nyimbi/tilemill,MappingKat/tilemill,nyimbi/tilemill,tizzybec/tilemill,florianf/tileoven,nyimbi/tilemill,fxtentacle/tilemill,nyimbi/tilemill,MappingKat/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,mbrukman/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,fxtentacle/tilemill,fxtentacle/tilemill,Zhao-Qi/tilemill,florianf/tileoven,tizzybec/tilemill,florianf/tileoven,Teino1978-Corp/Teino1978-Corp-tilemill,isaacs/tilemill,MappingKat/tilemill,MappingKat/tilemill,tizzybec/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,fxtentacle/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,tilemill-project/tilemill,nyimbi/tilemill