chase after vs crack onto

chase after

verb
  • To pursue someone with romantic intentions; to woo. 

  • Used other than figuratively or idiomatically: see chase, after. 

crack onto

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

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