gentlemen's room vs ladies' room

gentlemen's room

noun
  • A waiting room in a railway station or other public building, often including a separate lavatory. 

  • Any room intended for use by men 

ladies' room

noun
  • A waiting room in a railway station or other public building intended exclusively for women and usually including a separate women's lavatory. 

  • A room belonging to or intended for some or all women 

  • A public lavatory intended for use by women. 

How often have the words gentlemen's room and ladies' room occurred in a corpus of books? (source: Google Ngram Viewer )