Remove Encoding-enum from dart:io and add interface in dart:convert.

sdk/lib/_internal/pub/test/test_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.
 
 /// Test infrastructure for testing pub. Unlike typical unit tests, most pub
 /// tests are integration tests that stage some stuff on the file system, run
 /// pub, and then validate the results. This library provides an API to build
 /// tests like that.
 library test_pub;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 import 'dart:json' as json;
 import 'dart:math';
 
 import 'package:http/testing.dart';
 import 'package:path/path.dart' as path;
 import 'package:scheduled_test/scheduled_process.dart';
 import 'package:scheduled_test/scheduled_server.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 import 'package:unittest/compact_vm_config.dart';
@@ skipping 472 matching lines @@
 /// A subclass of [ScheduledProcess] that parses pub's verbose logging output
 /// and makes [nextLine], [nextErrLine], [remainingStdout], and
 /// [remainingStderr] work as though pub weren't running in verbose mode.
 class PubProcess extends ScheduledProcess {
   Stream<Pair<log.Level, String>> _log;
   Stream<String> _stdout;
   Stream<String> _stderr;
 
   PubProcess.start(executable, arguments,
       {workingDirectory, environment, String description,
-       Encoding encoding: Encoding.UTF_8})
+       Encoding encoding: UTF8})
     : super.start(executable, arguments,
         workingDirectory: workingDirectory,
         environment: environment,
         description: description,
         encoding: encoding);
 
   Stream<Pair<log.Level, String>> _logStream() {
     if (_log == null) {
       _log = mergeStreams(
         _outputToLog(super.stdoutStream(), log.Level.MESSAGE),
@@ skipping 273 matching lines @@
   bool matches(item, Map matchState) {
     if (item is! Pair) return false;
     return _firstMatcher.matches(item.first, matchState) &&
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }