Install barback from a hosted source in all tests.

test/build/outputs_error_to_json_test.dart

 // Copyright (c) 2014, 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 file.
 
 // Dart2js can take a long time to compile dart code, so we increase the timeout
 // to cope with that.
 @Timeout.factor(3)
 
 import 'package:pub/src/exit_codes.dart' as exit_codes;
 import 'package:scheduled_test/scheduled_test.dart';
@@ skipping 10 matching lines @@
   RewriteTransformer.asPlugin();
 
   String get allowedExtensions => '.txt';
 
   Future apply(Transform transform) => throw new Exception('oh no!');
 }
 """;
 
 main() {
    integration("outputs error to JSON in a failed build", () {
+     serveBarback();
+
      d.dir(appPath, [
        d.pubspec({
          "name": "myapp",
-         "transformers": ["myapp"]
+         "transformers": ["myapp"],
+         "dependencies": {"barback": "any"}
        }),
        d.dir("lib", [
          d.file("transformer.dart", TRANSFORMER)
        ]),
        d.dir("web", [
          d.file("foo.txt", "foo")
        ])
      ]).create();
 
-     createLockFile('myapp', pkg: ['barback']);
-
+     pubGet();
      schedulePub(args: ["build", "--format", "json"],
          outputJson: {
            "buildResult": "failure",
            "errors": [
              {
                "error": startsWith("Transform Rewrite on myapp|web/foo.txt "
                    "threw error: oh no!")
              }
            ],
            "log": []
          },
          exitCode: exit_codes.DATA);
    });
 }