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

sdk/lib/_internal/pub/bin/pub.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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
+import 'package:http/http.dart' as http;
 import 'package:path/path.dart' as path;
 import 'package:stack_trace/stack_trace.dart';
 
 import '../lib/src/command.dart';
 import '../lib/src/exit_codes.dart' as exit_codes;
 import '../lib/src/http.dart';
 import '../lib/src/io.dart';
 import '../lib/src/log.dart' as log;
 import '../lib/src/sdk.dart' as sdk;
 import '../lib/src/utils.dart';
@@ skipping 110 matching lines @@
   }).then((_) {
     // Explicitly exit on success to ensure that any dangling dart:io handles
     // don't cause the process to never terminate.
     return flushThenExit(exit_codes.SUCCESS);
   });
 }
 
 /// Returns the appropriate exit code for [exception], falling back on 1 if no
 /// appropriate exit code could be found.
 int chooseExitCode(exception) {
-  if (exception is HttpException || exception is HttpException ||
+  if (exception is HttpException || exception is http.ClientException ||
       exception is SocketException || exception is PubHttpException) {
     return exit_codes.UNAVAILABLE;
   } else if (exception is FormatException || exception is DataException) {
     return exit_codes.DATA;
   } else if (exception is UsageException) {
     return exit_codes.USAGE;
   } else {
     return 1;
   }
 }
@@ skipping 58 matching lines @@
     if (Platform.operatingSystem != 'windows') return null;
 
     return runProcess('ver', []).then((result) {
       if (result.stdout.join('\n').contains('XP')) {
         log.error('Sorry, but pub is not supported on Windows XP.');
         return flushThenExit(exit_codes.USAGE);
       }
     });
   });
 }