Green’s Dictionary of Slang

chocolate frog n.

[rhy. sl.]
(Aus.)

1. an informer [= dog n.2 (6b)].

[Aus]Tupper & Wortley Aus. Prison Sl. Gloss. [Internet] Chocolate frog. 1. An informer. Rhyming slang for ‘dog’.
[Aus]G. Seal Lingo 91: Then there are those things that form the basis for still more distinctively Australian rhymes, including: [...] chocolate frog for dog, underworld slang for an informer.

2. an immigrant from Southern Europe [= wog n.1 (8)].

[Aus]R. Aven-Bray Ridgey-Didge Oz Jack Lang 22: Chocolate Frog Wog.
[Aus]Tupper & Wortley Aus. Prison Sl. Gloss. [Internet] Chocolate frog. 2. A person of non-Anglo background. Rhyming slang for wog.
[Aus]G. Seal Lingo 91: Then there are those things that form the basis for still more distinctively Australian rhymes, including: [...] chocolate frogs for wogs (migrants from southern Europe).