Rip out dart:io from pkg/http wherever possible.

pkg/http/test/http_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library http_test;
 
 import 'package:http/http.dart' as http;
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
@@ skipping 280 matching lines @@
             'user-agent': ['Dart'],
             'x-random-header': ['Value'],
             'x-other-header': ['Other Value']
           },
         }))));
       }), completes);
     });
 
     test('read throws an error for a 4** status code', () {
       expect(startServer().then((_) {
-        expect(http.read(serverUrl.resolve('/error')), throwsHttpException);
+        expect(http.read(serverUrl.resolve('/error')), throwsClientException);
       }), completes);
     });
 
     test('readBytes', () {
       expect(startServer().then((_) {
         var future = http.readBytes(serverUrl, headers: {
           'X-Random-Header': 'Value',
           'X-Other-Header': 'Other Value',
           'User-Agent': 'Dart'
         }).then((bytes) => new String.fromCharCodes(bytes));
 
         expect(future, completion(parse(equals({
           'method': 'GET',
           'path': '/',
           'headers': {
             'content-length': ['0'],
             'accept-encoding': ['gzip'],
             'user-agent': ['Dart'],
             'x-random-header': ['Value'],
             'x-other-header': ['Other Value']
           },
         }))));
       }), completes);
     });
 
     test('readBytes throws an error for a 4** status code', () {
       expect(startServer().then((_) {
-        expect(http.readBytes(serverUrl.resolve('/error')), throwsHttpException);
+        expect(http.readBytes(serverUrl.resolve('/error')),
+            throwsClientException);
       }), completes);
     });
   });
 }