Make sure to drain stderr in tests so that spawned process doesn't hang.

utils/pub/io.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.
 
 /**
  * Helper functionality to make working with IO easier.
  */
 library io;
 
 import 'dart:io';
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   }
 
   var completer = new Completer<String>();
   var buffer = new StringBuffer();
   stream.onClosed = () => completer.complete(buffer.toString());
   stream.onData = () => buffer.add(stream.read());
   stream.onError = (e) => completer.completeException(e, stackTrace);
   return completer.future;
 }
 
+/// Wrap an InputStream in a ListInputStream. This eagerly drains the [source]
+/// input stream. This is useful for spawned processes which will not exit until
+/// their output streams have been drained.
+/// TODO(rnystrom): Get rid of this once #7218 is fixed.
+InputStream wrapInputStream(InputStream source) {
+  var sink = new ListInputStream();
+  // TODO(nweiz): Due to issuee 3657, pipeInputToInput naturally avoids calling
+  // both onClosed and onError. If 3657 gets fixed before 7013, we'll need to do
+  // that explicitly.
+  pipeInputToInput(source, sink);
+  return sink;
+}
+
 /// Spawns and runs the process located at [executable], passing in [args].
 /// Returns a [Future] that will complete with the results of the process after
 /// it has ended.
 ///
 /// The spawned process will inherit its parent's environment variables. If
 /// [environment] is provided, that will be used to augment (not replace) the
 /// the inherited variables.
 Future<PubProcessResult> runProcess(String executable, List<String> args,
     {workingDir, Map<String, String> environment}) {
   return _doProcess(Process.run, executable, args, workingDir, environment)
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   return new Directory(entry);
 }
 
 /**
  * Gets a [Uri] for [uri], which can either already be one, or be a [String].
  */
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return new Uri.fromString(uri);
 }