Get codebase ready for actually supporting versioning.

utils/pub/utils.dart

Index: utils/pub/utils.dart
diff --git a/utils/pub/utils.dart b/utils/pub/utils.dart
index d0c2f435d21de48cd5cefdfb5a116148f503931d..fe546113ed65a65852b565c79674fad7cb85a124 100644
--- a/utils/pub/utils.dart
+++ b/utils/pub/utils.dart
@@ -7,6 +7,15 @@
  */
 #library('pub_utils');
 
+/** Thrown by methods that parse text when the text isn't a valid. */
+class FormatException implements Exception {
+  final String message;
+
+  FormatException(this.message);
+
+  String toString() => message;
+}
+
 // TODO(rnystrom): Move into String?
 /** Pads [source] to [length] by adding spaces at the end. */
 String padRight(String source, int length) {