chat up vs crack onto

chat up

verb
  • To talk to (someone) in a friendly, open, or casual manner, sometimes also in a charming or affected manner, usually to curry favor, and sometimes flirtatiously with the intention of establishing a romantic or sexual encounter or relationship with that person. 

crack onto

verb
  • To flirt with; to approach and speak to (someone), seeking romance, love, sex, etc. 

How often have the words chat up and crack onto occurred in a corpus of books? (source: Google Ngram Viewer )