Get rid of RootSource.

utils/pub/sdk.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.
 
 /// Operations relative to the user's installed Dart SDK.
 library sdk;
 
 import 'dart:io';
 
 import '../../pkg/path/lib/path.dart' as path;
@@ skipping 27 matching lines @@
 /// Determine the SDK's version number.
 Version _getVersion() {
   var revisionPath = path.join(rootDirectory, "version");
   var version = new File(revisionPath).readAsStringSync().trim();
 
   // Given a version file like: 0.1.2.0_r17495
   // We create a semver like:   0.1.2+0._r17495
   var match = _versionPattern.firstMatch(version);
   if (match == null) {
     throw new FormatException("The Dart SDK's 'version' file was not in a "
-        "format pub could recognize. Found: $revision");
+        "format pub could recognize. Found: $version");
   }
 
   var build = match[4];
   if (match[5].length > 0) build = '$build.${match[5]}';
 
   return new Version(
       int.parse(match[1]), int.parse(match[2]), int.parse(match[3]),
       build: build);
 }