Switch pkg packages, pub, and dartdoc to use package: imports.

sdk/lib/_internal/dartdoc/lib/universe_serializer.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 library serializes the Dart2Js AST into a compact and easy to use
  * [Element] tree useful for code exploration tools such as DartDoc.
  */
 library universe_serializer;
 
 import 'dartdoc.dart';
 
 // TODO(rnystrom): Use "package:" URL (#4968).
-import '../../../../../pkg/pathos/lib/path.dart' as path;
+import 'package:pathos/path.dart' as path;
 import '../../compiler/implementation/mirrors/dart2js_mirror.dart' as dart2js;
 import '../../compiler/implementation/mirrors/mirrors.dart';
 import '../../compiler/implementation/mirrors/mirrors_util.dart';
 import '../../libraries.dart';
 
 String _stripUri(String uri) {
   String prefix = "/dart/";
   int start = uri.indexOf(prefix);
   if (start != -1) {
     return uri.substring(start + prefix.length);
@@ skipping 498 matching lines @@
   Reference.fromElement(LibraryElement e) : name = e.name, refId = e.id;
 
   static String getId(Mirror mirror) {
     String id = _escapeId(mirror.simpleName);
     if (mirror.owner != null) {
       id = '${getId(mirror.owner)}/$id';
     }
     return id;
   }
 }