Need to override application/json default content decoder to UTF-8

[domesticmouse]

I have a sample app that makes http get requests to Unsplash's API. The results are in the form of application/json, encoded in UTF-8. Unfortunately, the content-type on the return is application/json, not application/json; charset=utf-8.

See flutter/samples#586 for details.

Ask: allow overriding the default content type charset to UTF-8. Or, ignore the standard and make UTF-8 the default as it's what most people expect, and I suspect what web browsers do by default.

[DeD1rk]

See the discussion in #175. Indeed I believe http should change to strictly use UTF-8 for json by default.

[natebosch]

I do think we should consider this.

In the mean time, the expected pattern is jsonDecode(utf8.decode(response.bodyBytes)), not jsonDecode(response.body).

[natebosch]

Closing in favor of #175