Show better error messages in network failures.

utils/pub/source.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 source;
 
 import 'io.dart';
 import 'package.dart';
 import 'pubspec.dart';
 import 'system_cache.dart';
 import 'version.dart';
 
 /**
  * A source from which to install packages.
  *
  * Each source has many packages that it looks up using [PackageId]s. The source
  * is responsible for installing these packages to the package cache.
  */
 abstract class Source {
   /**
    * The name of the source. Should be lower-case, suitable for use in a
    * filename, and unique accross all sources.
    */
   abstract String get name;
 
+  /// Whether or not this source is the default source.
+  bool get isDefault => systemCache.sources.defaultSource == this;
+
   /**
    * Whether this source's packages should be cached in Pub's global cache
    * directory.
    *
    * A source should be cached if it requires network access to retrieve
    * packages. It doesn't need to be cached if all packages are available
    * locally.
    */
   abstract bool get shouldCache;
 
@@ skipping 146 matching lines @@
    * resolved id.
    *
    * The returned [PackageId] may have a description field that's invalid
    * according to [validateDescription], although it must still be serializable
    * to JSON and YAML. It must also be equal to [id] according to
    * [descriptionsEqual].
    *
    * By default, this just returns [id].
    */
   Future<PackageId> resolveId(PackageId id) => new Future.immediate(id);
+
+  /// Returns the source's name.
+  String toString() => name;
 }