pkg/http: fixed analyzer warnings

pkg/http/lib/src/utils.dart

 // Copyright (c) 2012, 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 utils;
 
 import 'dart:async';
 import 'dart:convert';
-import 'dart:io';
 import 'dart:typed_data';
 
 import 'package:stack_trace/stack_trace.dart';
 
 import 'byte_stream.dart';
 
 /// Converts a URL query string (or `application/x-www-form-urlencoded` body)
 /// into a [Map] from parameter names to values.
 ///
 ///     queryToMap("foo=bar&baz=bang&qux");
@@ skipping 174 matching lines @@
 }
 
 /// Configures [future] so that its result (success or exception) is passed on
 /// to [completer].
 void chainToCompleter(Future future, Completer completer) {
   future.then(completer.complete, onError: completer.completeError);
 }
 
 /// Like [Future.sync], but wraps the Future in [Chain.track] as well.
 Future syncFuture(callback()) => Chain.track(new Future.sync(callback));