Get rid of #source in pub.

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('package.dart');
+#import('source_registry.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.
  */
 class SystemCache {
   /**
    * The root directory where this package cache is located.
    */
@@ skipping 62 matching lines @@
         throw 'Package ${id.fullName} not found in source "${id.source.name}".';
       }
       return Package.load(path, sources);
     });
 
     always(future, () => _pendingInstalls.remove(id));
     _pendingInstalls[id] = future;
     return future;
   }
 }