fix accidental breaking changes in html5lib, deprecate instead

pkg/third_party/html5lib/lib/dom.dart

Index: pkg/third_party/html5lib/lib/dom.dart
diff --git a/pkg/third_party/html5lib/lib/dom.dart b/pkg/third_party/html5lib/lib/dom.dart
index 66fa1b364c74ff60c67b54e6d7784868bbbcc961..6fceb65acb602c2a140b8531a43c6a07dcb7b73d 100644
--- a/pkg/third_party/html5lib/lib/dom.dart
+++ b/pkg/third_party/html5lib/lib/dom.dart
@@ -154,6 +154,12 @@ abstract class Node {
 
   int get nodeType;
 
+  /** *Deprecated* use [text], [Text.data] or [Comment.data]. */
+  @deprecated String get value => null;
+
+  /** *Deprecated* use [nodeType]. */
+  @deprecated int get $dom_nodeType => nodeType;
+
   String get outerHtml {
     var str = new StringBuffer();
     _addOuterHtml(str);
@@ -433,6 +439,10 @@ class Text extends Node {
 
   Text(this.data) : super(null);
 
+  /** *Deprecated* use [data]. */
+  @deprecated String get value => data;
+  @deprecated set value(String x) { data = x; }
+
   int get nodeType => Node.TEXT_NODE;
 
   String toString() => '"$data"';