Add Element.endSourceSpan

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';
@@ skipping 60 matching lines @@
   final String defaultNamespace;
 
   Document document;
 
   final List<Element> openElements = <Element>[];
 
   final activeFormattingElements = new ActiveFormattingElements();
 
   Node headPointer;
 
-  Node formPointer;
+  Element formPointer;
 
   /// Switch the function used to insert an element from the
   /// normal one to the misnested table one and back again
   bool insertFromTable;
 
   TreeBuilder(bool namespaceHTMLElements)
       : defaultNamespace = namespaceHTMLElements ? Namespaces.html : null {
     reset();
   }
 
@@ skipping 307 matching lines @@
   Document getDocument() => document;
 
   /// Return the final fragment.
   DocumentFragment getFragment() {
     //XXX assert innerHTML
     var fragment = new DocumentFragment();
     openElements[0].reparentChildren(fragment);
     return fragment;
   }
 }