The word 'chintz' refers to a multicoloured cotton fabric, with a glazed finish. The word is Hindi in origin and dates from the early 17th century. The Hindi word 'chint' means a 'spattering' or 'stain'.
When it comes to 'chintzy', British and American English diverge. In Britain it is still connected to fabric. 'A pretty chintzy pattern'.
In North America it connotes cheapness and poor quality.
Having read @Terpsichore's answer I have significantly edited this one, having earlier taken Raymond Chandler to have been an American. However he would appear to have spent his young life in Britain, having been educated at Dulwich college. And this fact suggests his usage here was more a British one. So I accept Terpsichore's view and have upvoted that answer.