Use "package:" imports for pub.

test/list_package_dirs/ignores_updated_pubspec_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 d.file.
 
 import 'package:path/path.dart' as path;
+import 'package:pub/src/io.dart';
 
-import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
   integration("uses what's in the lockfile regardless of the pubspec", () {
     d.dir("foo", [
       d.libDir("foo"),
       d.libPubspec("foo", "1.0.0")
     ]).create();
@@ skipping 23 matching lines @@
             "foo": path.join(sandboxDir, "foo", "lib"),
             "myapp": canonicalize(path.join(sandboxDir, appPath, "lib"))
           },
           "input_files": [
             canonicalize(path.join(sandboxDir, appPath, "pubspec.lock")),
             canonicalize(path.join(sandboxDir, appPath, "pubspec.yaml"))
           ]
         });
   });
 }