http get can't solve response error : Invalid media type

_From @DuanTzXavier on July 17, 2018 7:32_

Come from flutter！on **MacOS**

### Logs

```
07-14 01:59:51.068 2137-2153/top.basking.calculator I/flutter: 200
07-14 01:59:51.068 2137-2153/top.basking.calculator I/flutter: {connection: keep-alive, content-type: application/json; charset=utf-8;, transfer-encoding: chunked, date: Fri, 13 Jul 2018 17:59:15 GMT, server: nginx}
07-14 01:59:51.070 2137-2153/top.basking.calculator E/flutter: [ERROR:topaz/lib/tonic/logging/dart_error.cc(16)] Unhandled exception:
Error on line 1, column 33: Invalid media type: expected /[^()<>@,;:"\\\/[\]?={} \t\x00-\x1F\x7F]+/.
application/json; charset=utf-8;
^
#0 wrapFormatException (package:http_parser/src/utils.dart:15:5)
#1 new MediaType.parse (package:http_parser/src/media_type.dart:46:12)
#2 _contentTypeForHeaders (package:http/src/response.dart:93:39)
#3 _encodingForHeaders (package:http/src/response.dart:86:22)
#4 Response.body (package:http/src/response.dart:27:22)
#5 ExchangeCalculatorScreenState.loadData (package:calculator/screens/ExchangeCalculatorScreen.dart:465:20)

```

### Code

```Dart
var dataURL = "http://api.k780.com?app=finance.rate&scur=CNY&tcur=GBP&appkey=35134&sign=fb020c3129435bb5ff21b7113e9cb1c1&format=json";
print(dataURL);
var response = await http.get(
dataURL);
print(response.statusCode);
print(response.headers);
print(response.body);
```
can't resolve response.body

but when I use UTF8Codec class resolve bodybytes ,it works!

```Dart
print(Utf8Codec().decode(response.bodyBytes));
```
here is success log:
```
{"success":"1","result":{"status":"ALREADY","scur":"CNY","tcur":"GBP","ratenm":"人民币/英镑","rate":"0.113045","update":"2018-07-13 23:28:01"}}
```

here is part of my `flutter doctor -v `

```
[✓] Flutter (Channel beta, v0.5.1, on Mac OS X 10.13.5 17F77, locale en-NZ)
• Flutter version 0.5.1 at /Users/tzduan/development/flutter
• Framework revision c7ea3ca377 (6 weeks ago), 2018-05-29 21:07:33 +0200
• Engine revision 1ed25ca7b7
• Dart version 2.0.0-dev.58.0.flutter-f981f09760
```

by the way, How to specific config dart sdk in flutter?
flutter always use cache dart sdk....

_Copied from original issue: dart-lang/sdk#33881_