Roll Observatory packages and add a roll script

packages/html/lib/src/treebuilder.dart

 /// Internals to the tree builders.
 library treebuilder;
 
 import 'dart:collection';
 import 'package:html/dom.dart';
 import 'package:html/parser.dart' show getElementNameTuple;
 import 'package:source_span/source_span.dart';
 import 'constants.dart';
 import 'list_proxy.dart';
 import 'token.dart';
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   Document getDocument() => document;
 
   /// Return the final fragment.
   DocumentFragment getFragment() {
     //XXX assert innerHTML
     var fragment = new DocumentFragment();
     openElements[0].reparentChildren(fragment);
     return fragment;
   }
 }