First stab at a dev server in pub using barback.

sdk/lib/_internal/pub/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.
 
 /// Generic utility functions. Stuff that should possibly be in core.
 library pub.utils;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
@@ skipping 54 matching lines @@
       completed = true;
       _completer.completeError(e);
     }));
 
     return task;
   }
 
   Future<List> get future => _completer.future;
 }
 
+/// Returns [posix] on POSIX machines and [windows] on Windows.
+///
+/// If [windows] is omitted, returns `""` on Windows.
+String getPlatformString(String posix, [String windows]) {
+  if (windows == null) windows = "";
+  return Platform.operatingSystem == "windows" ? windows : posix;
+}
+
 /// Like [new Future], but avoids around issue 11911 by using [new Future.value]
 /// under the covers.
 Future newFuture(callback()) => new Future.value().then((_) => callback());
 
 // TODO(rnystrom): Move into String?
 /// Pads [source] to [length] by adding spaces at the end.
 String padRight(String source, int length) {
   final result = new StringBuffer();
   result.write(source);
 
@@ skipping 413 matching lines @@
     error is DirectoryException ||
     error is FileException ||
     error is HttpException ||
     error is HttpException ||
     error is LinkException ||
     error is OSError ||
     error is ProcessException ||
     error is SocketException ||
     error is WebSocketException;
 }