pkg/third_party/html5lib: lots of cleanup

pkg/third_party/html5lib/lib/dom.dart

 /**
  * A simple tree API that results from parsing html. Intended to be compatible
  * with dart:html, but right now it resembles the classic JS DOM.
  */
 library dom;
 
 import 'dart:collection';
 import 'package:source_maps/span.dart' show FileSpan;
 
 import 'src/constants.dart';
 import 'src/list_proxy.dart';
 import 'src/token.dart';
 import 'src/tokenizer.dart';
-import 'src/treebuilder.dart';
 import 'src/utils.dart';
 import 'dom_parsing.dart';
 import 'parser.dart';
 
 // TODO(jmesserly): this needs to be replaced by an AttributeMap for attributes
 // that exposes namespace info.
 class AttributeName implements Comparable {
   /** The namespace prefix, e.g. `xlink`. */
   final String prefix;
 
@@ skipping 396 matching lines @@
   String value;
 
   Text(this.value) : super(null);
 
   int get nodeType => Node.TEXT_NODE;
 
   String toString() => '"$value"';
 
   void _addOuterHtml(StringBuffer str) {
     // Don't escape text for certain elements, notably <script>.
-    if (rcdataElements.contains(parent.tagName) ||
+    if (RCDATA_ELEMENTS.contains(parent.tagName) ||
         parent.tagName == 'plaintext') {
       str.write(value);
     } else {
       str.write(htmlSerializeEscape(value));
     }
   }
 
   Text clone() => new Text(value);
 }
 
@@ skipping 422 matching lines @@
     if (start == null) start = length - 1;
     return _filtered.lastIndexOf(element, start);
   }
 
   Element get first => _filtered.first;
 
   Element get last => _filtered.last;
 
   Element get single => _filtered.single;
 }