Fix dartdoc to dart2js path in SDK

pkg/dartdoc/dartdoc.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.
 
 /**
  * To generate docs for a library, run this script with the path to an
  * entrypoint .dart file, like:
  *
  *     $ dart dartdoc.dart foo.dart
  *
@@ skipping 213 matching lines @@
  * path to the directory containing `dartdoc.dart`. If you're running a script
  * that imports dartdoc, it will be the path to that script.
  */
 // TODO(johnniwinther): Convert to final (lazily initialized) variables when
 // the feature is supported.
 Path get scriptDir() =>
     new Path.fromNative(new Options().script).directoryPath;
 
 // TODO(johnniwinther): Trailing slashes matter due to the use of [libPath] as
 // a base URI with [Uri.resolve].
+/// Relative path to the library in which dart2js resides.
 Path get libPath() => IN_SDK
-    ? scriptDir.append('../dart2js/')
+    ? scriptDir.append('../../lib/dart2js/')
     : scriptDir.append('../../');
 
 /**
  * Deletes and recreates the output directory at [path] if it exists.
  */
 void cleanOutputDirectory(Path path) {
   final outputDir = new Directory.fromPath(path);
   if (outputDir.existsSync()) {
     outputDir.deleteRecursivelySync();
   }
@@ skipping 1338 matching lines @@
   }
 
   /**
    * Returns [:true:] if [type] should be regarded as an exception.
    */
   bool isException(TypeMirror type) {
     return type.simpleName.endsWith('Exception');
   }
 }