Green’s Dictionary of Slang

1. an informer [= dog n.² (6b)].

1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Chocolate frog. 1. An informer. Rhyming slang for ‘dog’.
1999		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.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 42/1: chocolate frog n. an informer.

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

1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 22: Chocolate Frog Wog.
1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Chocolate frog. 2. A person of non-Anglo background. Rhyming slang for wog.
1999		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).