Update pub to use the latest dart:io stream APIs.

utils/tests/pub/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;
 
@@ skipping 1421 matching lines @@
       return timeout(_stderrFuture.then((stream) => stream.toList())
               .then((lines) => lines.join("\n")),
           _SCHEDULE_TIMEOUT,
           "waiting for the last stderr line from process $name");
     });
   }
 
   /// Writes [line] to the process as stdin.
   void writeLine(String line) {
     _schedule((_) => _processFuture.then(
-        (p) => p.stdin.writeln('$line')));
+        (p) => p.stdin.add(encodeUtf8('$line\n'))));
   }
 
   /// Kills the process, and waits until it's dead.
   void kill() {
     _endScheduled = true;
     _schedule((_) {
       _endExpected = true;
       _process.kill();
       timeout(_exitCodeFuture, _SCHEDULE_TIMEOUT,
           "waiting for process $name to die");
@@ skipping 180 matching lines @@
 /// calling [completion] is unnecessary.
 void expectLater(Future actual, matcher, {String reason,
     FailureHandler failureHandler, bool verbose: false}) {
   _schedule((_) {
     return actual.then((value) {
       expect(value, matcher, reason: reason, failureHandler: failureHandler,
           verbose: false);
     });
   });
 }