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

pkg/http/test/utils.dart

Index: pkg/http/test/utils.dart
diff --git a/pkg/http/test/utils.dart b/pkg/http/test/utils.dart
index ba516c95886b797ab7f7ff217c7c2a376fffbe4a..051cbd4f0936d56265c336d4613b63981ee6c58e 100644
--- a/pkg/http/test/utils.dart
+++ b/pkg/http/test/utils.dart
@@ -8,7 +8,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
-import 'package:http/src/byte_stream.dart';
+import 'package:http/http.dart';
 import 'package:http/src/utils.dart';
 import 'package:unittest/unittest.dart';
 
@@ -174,17 +174,9 @@ class _Parse extends Matcher {
   }
 }
 
-/// A matcher for HttpExceptions.
-const isHttpException = const _HttpException();
-
 /// A matcher for functions that throw HttpException.
-const Matcher throwsHttpException =
-    const Throws(isHttpException);
-
-class _HttpException extends TypeMatcher {
-  const _HttpException() : super("HttpException");
-  bool matches(item, Map matchState) => item is HttpException;
-}
+Matcher get throwsClientException =>
+    throwsA(new isInstanceOf<ClientException>());
 
 /// A matcher for RedirectLimitExceededExceptions.
 const isRedirectLimitExceededException =