pkg/csslib: types, fixes, cleanup

pkg/csslib/lib/src/validate.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 csslib.src.validate;
 
-import 'package:csslib/parser.dart';
 import 'package:csslib/visitor.dart';
 import 'package:source_maps/span.dart' show Span;
 
 /** Can be thrown on any Css runtime problem includes source location. */
 class CssSelectorException implements Exception {
   final String _message;
   final Span _span;
 
   CssSelectorException(this._message, [this._span]);
 
@@ skipping 108 matching lines @@
       }
     }
 
     // Every selector must match.
     Selector selector = selectors[0];
     assert((matches >= 0 ? matches : -matches) ==
         selector.simpleSelectorSequences.length);
   }
 }