Move Python script over to Dart.

CONTRIBUTING.md

@@ -42,7 +42,7 @@ Getting the code and configuring your environment
  * `git remote add upstream git@github.com:flutter/flutter.git` (So that you
    fetch from the master repository, not your clone, when running `git fetch`
    et al.)
- * Run `./dev/update_packages.py` This will fetch all the Dart packages that
+ * Run `dart ./dev/update_packages.dart` This will fetch all the Dart packages that
    Flutter depends on. You can replicate what this script does by running
    `pub get` in each directory that contains a `pubspec.yaml` file.
  * Add this repository's `bin` directory to your path. That will let you use the

dev/update_packages.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:io';
+
+final String binaryName = Platform.isWindows ? 'pub.bat' : 'pub';
+update(Directory directory) {
+  for (FileSystemEntity dir in directory.listSync()) {
+    if (dir is Directory) {
+      print("Updating ${dir.path}...");
+      Process.runSync(binaryName, ['get'], workingDirectory: dir.path);
+    }
+  }
+}
+
+main() {
+  String FLUTTER_ROOT = new File(Platform.script.toFilePath()).parent.parent.path;
+  update(new Directory("$FLUTTER_ROOT/packages"));
+  update(new Directory("$FLUTTER_ROOT/examples"));
+}

dev/update_packages.py

-#!/usr/bin/env python
-# Copyright 2015 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-import os
-import subprocess
-
-FLUTTER_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
-
-def update(directory):
-    packages = sorted(os.listdir(directory))
-    for package in packages:
-        package_dir = os.path.join(directory, package)
-        if os.path.isdir(package_dir):
-            print 'Updating', package, '...'
-            subprocess.check_call(['pub', 'get'], cwd=package_dir)
-
-update(os.path.join(FLUTTER_ROOT, 'packages'))
-update(os.path.join(FLUTTER_ROOT, 'examples'))