gentlemen's room vs women's 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 

women's 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. 

  • Synonym of ladies' room: a public lavatory intended for women. 

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