Add support for pub install.

utils/pub/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');
 
 // 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.add(source);
 
   while (result.length < length) {
     result.add(' ');
   }
 
   return result.toString();
-}
+}
+
+/**
+ * Runs [fn] after [future] completes, whether it completes successfully or not.
+ * Essentially an asynchronous `finally` block.
+ */
+always(Future future, fn()) {
+  var completer = new Completer();
+  future.then((_) => fn());
+  future.handleException((_) {
+    fn();
+    return false;
+  });
+}
+
+/**
+ * Flattens nested lists into a single list containing only non-list elements.
+ */
+List flatten(List nested) {
+  var result = [];
+  helper(list) {
+    for (var element in list) {
+      if (element is List) {
+        helper(element);
+      } else {
+        result.add(element);
+      }
+    }
+  }
+  helper(nested);
+  return result;
+}