this isnt evidence, its speculative and uses references that are circular and self referencing. i'd expect (and did look up before posting) clear refernce to its history as a derogatroy term, but this is missing.
http://www.nwasianweekly.com/2011/09/racial-slurs-chink/ - Someone discussing their childhood after emigrating to America.
I know wikipedia is scoffed at but the history section mentioning it was first known printed use was 1878 cites Tom Dalzell, Terry Victor, ed. (2005-05-12). New Partridge Dictionary of Slang and Unconventional English. Routledge. ISBN 978-0-415-21258-8, which sounds to me like a more reliable source. Although that is just a use of the word without any indication of whether it was used in a derogatory fashion or not, it shows historical use, that is evidence of it's use around the time of the other suggestions of it's possible origin.