Roll Observatory packages and add a roll script

packages/html/lib/src/query_selector.dart

 /// Query selector implementation for our DOM.
 library html.src.query;
 
 import 'package:csslib/parser.dart' as css;
 import 'package:csslib/parser.dart' show TokenKind;
 import 'package:csslib/visitor.dart'; // the CSSOM
 import 'package:html/dom.dart';
 import 'package:html/src/constants.dart' show isWhitespaceCC;
 
 bool matches(Node node, String selector) =>
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         return value.startsWith(select);
       case TokenKind.SUFFIX_MATCH:
         return value.endsWith(select);
       case TokenKind.SUBSTRING_MATCH:
         return value.contains(select);
       default:
         throw _unsupported(selector);
     }
   }
 }