Install barback from a hosted source in all tests.

test/snapshot/doesnt_load_irrelevant_transformers_test.dart

 // Copyright (c) 2014, 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 pub_tests;
 
 import 'package:path/path.dart' as p;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 const BROKEN_TRANSFORMER = """
 import 'dart:async';
 
 import 'package:barback/barback.dart';
 
 class BrokenTransformer extends Transformer {
   BrokenTransformer.asPlugin();
 
   // This file intentionally has a syntax error so that any attempt to load it
   // will crash.
 """;
 
 main() {
   // Regression test for issue 20917.
   integration("snapshots the transformed version of an executable", () {
     servePackages((builder) {
-      builder.serveRepoPackage('barback');
+      builder.serveRealPackage('barback');
 
       builder.serve("foo", "1.2.3",
           contents: [
         d.dir("bin", [
           d.file("hello.dart", "void main() => print('hello!');")
         ])
       ]);
     });
 
     d.dir(appPath, [
@@ skipping 14 matching lines @@
 
     d.dir(p.join(appPath, '.pub', 'bin'), [
       d.dir('foo', [d.matcherFile('hello.dart.snapshot', contains('hello!'))])
     ]).validate();
 
     var process = pubRun(args: ['foo:hello']);
     process.stdout.expect("hello!");
     process.shouldExit();
   });
 }