Show the dependender(s) for missing packages.

sdk/lib/_internal/pub/test/pub_get_and_upgrade_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 pub_tests;
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import 'descriptor.dart' as d;
 import 'test_pub.dart';
@@ skipping 92 matching lines @@
       ]).create();
 
       d.dir(appPath, [
         d.appPubspec({
           "foo": {"path": "../deps/foo"},
           "bar": {"path": "../deps/bar"}
         })
       ]).create();
 
       pubCommand(command,
-          error: new RegExp("^Incompatible dependencies on 'baz':\n"));
+          error: new RegExp("^Incompatible dependencies on baz:\n"));
     });
 
     integration('does not allow a dependency on itself', () {
       d.dir(appPath, [
         d.appPubspec({
           "myapp": {"path": "."}
         })
       ]).create();
 
       pubCommand(command, error: new RegExp(r'"dependencies.myapp": Package '
           r'may not list itself as a dependency\.'));
     });
 
     integration('does not allow a dev dependency on itself', () {
       d.dir(appPath, [
         d.pubspec({
           "name": "myapp",
           "dev_dependencies": {
             "myapp": {"path": "."}
           }
         })
       ]).create();
 
       pubCommand(command, error: new RegExp(r'"dev_dependencies.myapp": '
           r'Package may not list itself as a dependency\.'));
     });
   });
 }