Fix pub on windows.

utils/pub/io.dart

Index: utils/pub/io.dart
diff --git a/utils/pub/io.dart b/utils/pub/io.dart
index 85a094cedab2953ab3cf2b0f9da8bf22fe1d5e21..82614ca68af23db08cc7fa8d07b6d62a2d14e5b0 100644
--- a/utils/pub/io.dart
+++ b/utils/pub/io.dart
@@ -81,8 +81,8 @@ String writeBinaryFile(String file, List<int> contents) {
 Future<String> createFileFromStream(Stream<List<int>> stream, String file) {
   log.io("Creating $file from stream.");
 
-  var stream = new File(file).openOutputStream();
-  return stream.pipe(wrapOutputStream(stream)).then((_) {
+  var outputStream = new File(file).openOutputStream();
+  return stream.pipe(wrapOutputStream(outputStream)).then((_) {
     log.fine("Created $file from stream.");
     return file;
   });