Add validation infrastructure for "pub lish".

utils/pub/system_cache.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 system_cache;
 
 import 'dart:io';
 
+import 'git_source.dart';
+import 'hosted_source.dart';
 import 'io.dart';
 import 'io.dart' as io show createTempDir;
 import 'package.dart';
+import 'sdk_source.dart';
 import 'source.dart';
 import 'source_registry.dart';
 import 'utils.dart';
 import 'version.dart';
 
 /**
  * The system-wide cache of installed packages.
  *
  * This cache contains all packages that are downloaded from the internet.
  * Packages that are available locally (e.g. from the SDK) don't use this cache.
@@ skipping 17 matching lines @@
   final SourceRegistry sources;
 
   /**
    * Creates a new package cache which is backed by the given directory on the
    * user's file system.
    */
   SystemCache(this.rootDir)
   : _pendingInstalls = new Map<PackageId, Future<Package>>(),
     sources = new SourceRegistry();
 
+  /// Creates a system cache and registers the standard set of sources.
+  factory SystemCache.withSources(String rootDir, String sdkDir) {
+    var cache = new SystemCache(rootDir);
+    cache.register(new SdkSource(sdkDir));
+    cache.register(new GitSource());
+    cache.register(new HostedSource());
+    cache.sources.setDefault('hosted');
+    return cache;
+  }
+
   /**
    * Registers a new source. This source must not have the same name as a source
    * that's already been registered.
    */
   void register(Source source) {
     source.bind(this);
     sources.register(source);
   }
 
   /**
@@ skipping 29 matching lines @@
   }
 
   /// Delete's the system cache's internal temp directory.
   Future deleteTempDir() {
     return dirExists(tempDir).chain((exists) {
       if (!exists) return new Future.immediate(null);
       return deleteDir(tempDir);
     });
   }
 }