adds file path source to pub

utils/pub/path_source.dart

Index: utils/pub/path_source.dart
diff --git a/utils/pub/path_source.dart b/utils/pub/path_source.dart
new file mode 100644
index 0000000000000000000000000000000000000000..ff34dd0e6ddcadbbf77633f62f9eeae8d7e30a13
--- /dev/null
+++ b/utils/pub/path_source.dart
@@ -0,0 +1,33 @@
+// 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.
+
+library path_source;
+
+import 'dart:async';
+import 'io.dart';
+import 'package.dart';
+import 'pubspec.dart';
+import 'version.dart';
+import 'source.dart';
+import 'dart:io';
+
+
+/// A package [Source] that installs packages from a given file path
+/// for development use.
+class PathSource extends Source {
+  final name = 'path';
+  final shouldCache = false;
+
+  Future<Pubspec> describe(PackageId id) =>
+    Package.load(id.name, id.description, systemCache.sources).then(
+        (pkg) => pkg.pubspec);
+
+  Future<bool> install(PackageId id, String path) =>
+    createPackageSymlink(id.name, id.description, path).then((_) => true);
+
+  void validateDescription(description, {bool fromLockFile: false}) {
+    if (description is! String)
+      throw new FormatException("The description must be a path string.");
+  }
+}