fix apidoc - we see errors when building it using build.py

utils/apidoc/apidoc.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.
 
 /**
  * This generates the reference documentation for the core libraries that come
  * with dart. It is built on top of dartdoc, which is a general-purpose library
  * for generating docs from any Dart code. This library extends that to include
  * additional information and styling specific to our standard library.
  *
@@ skipping 97 matching lines @@
   world.reset();
 
   // Add all of the core libraries.
   world.getOrAddLibrary('dart:core');
   world.getOrAddLibrary('dart:coreimpl');
   world.getOrAddLibrary('dart:crypto');
   world.getOrAddLibrary('dart:html');
   world.getOrAddLibrary('dart:io');
   world.getOrAddLibrary('dart:isolate');
   world.getOrAddLibrary('dart:json');
-  world.getOrAddLibrary('lib/unittest/unittest.dart');
+  world.getOrAddLibrary('${doc.scriptDir}/../../lib/unittest/unittest.dart');
   world.getOrAddLibrary('dart:uri');
   world.getOrAddLibrary('dart:utf');
   world.process();
 
   print('Generating docs...');
   final apidoc = new Apidoc(mdn, outputDir, mode, generateAppCache);
 
   Futures.wait([scriptCompiled, copiedStatic, copiedApiDocStatic]).then((_) {
     apidoc.document();
   });
@@ skipping 380 matching lines @@
           '''
           <p class="correspond">This corresponds to $domTypesText in the
           ${a("dom.html", "dart:dom_deprecated")} library.</p>
           ''';
     }
 
     return '';
   }
 
 }