convenience store vs pony keg

convenience store

noun
  • A small retail store, often in a residential area, that carries a limited selection of items such as staples, junk food, and drugstore items, and which is open long hours for the convenience of shoppers. 

pony keg

noun
  • A drive-through liquor store; by extension, any convenience store. 

  • A container for beer holding 7.75 US gallons, equal to half the size of a standard beer keg. 

How often have the words convenience store and pony keg occurred in a corpus of books? (source: Google Ngram Viewer )