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

utils/tests/pub/pubspec_test.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.
 
 library pubspec_test;
 
-import '../../../pkg/unittest/lib/unittest.dart';
-import 'test_pub.dart';
+import 'package:unittest/unittest.dart';
+
 import '../../pub/pubspec.dart';
 import '../../pub/source.dart';
 import '../../pub/source_registry.dart';
 import '../../pub/utils.dart';
 import '../../pub/version.dart';
+import 'test_pub.dart';
 
 class MockSource extends Source {
   final String name = "mock";
   final bool shouldCache = false;
   dynamic parseDescription(String filePath, description,
                            {bool fromLockFile: false}) {
     if (description != 'ok') throw new FormatException('Bad');
     return description;
   }
   String packageName(description) => 'foo';
@@ skipping 178 matching lines @@
 
       test("throws if the sdk isn't a valid version constraint", () {
         expectFormatError('''
 environment:
   sdk: "oopies"
 ''');
       });
     });
   });
 }