Beginning of CSS parser using frog parsering infrastructure.

utils/css/cssselectorexception.dart

+// Copyright (c) 2011, 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.
+
+// TODO(terry): Rename CompilerException to be SourceException then this
+//              exception would be derived from SourceException.
+
+/** Can be thrown on any Css runtime problem includes source location. */
+class CssSelectorException implements Exception {
+  final String _message;
+  final lang.SourceSpan _location;
+
+  CssSelectorException(this._message, [this._location = null]);
+
+  String toString() {
+    if (_location != null) {
+      return 'CssSelectorException: ${_location.toMessageString(_message)}';
+    } else {
+      return 'CssSelectorException: $_message';
+    }
+  }
+
+}