dob vs turn King's evidence

dob

noun
  • A small amount of something, especially paste. 

verb
  • To report (a person) to someone in authority for a wrongdoing. 

  • To play truant 

  • In the scouting movement, to chant dob to indicate that one will do one's best to follow the scouting laws. 

  • To nominate a person, often in their absence, for an unpleasant task. 

  • To do one's share; to contribute. 

turn King's evidence

How often have the words dob and turn King's evidence occurred in a corpus of books? (source: Google Ngram Viewer )