[html5lib] implement querySelector/querySelectorAll

pkg/third_party/html5lib/lib/dom_parsing.dart

Index: pkg/third_party/html5lib/lib/dom_parsing.dart
diff --git a/pkg/third_party/html5lib/lib/dom_parsing.dart b/pkg/third_party/html5lib/lib/dom_parsing.dart
index aed9fffe2378cd3f2146e0947f9120e6729faaf4..527d9a6fa917cc0e8cef0f4afbd46679f58ce348 100644
--- a/pkg/third_party/html5lib/lib/dom_parsing.dart
+++ b/pkg/third_party/html5lib/lib/dom_parsing.dart
@@ -40,8 +40,7 @@ class TreeVisitor {
 
   visitComment(Comment node) => visitNodeFallback(node);
 
-  // Note: visits document by default because DocumentFragment is a Document.
-  visitDocumentFragment(DocumentFragment node) => visitDocument(node);
+  visitDocumentFragment(DocumentFragment node) => visitNodeFallback(node);
 }
 
 /// Converts the DOM tree into an HTML string with code markup suitable for
@@ -166,7 +165,7 @@ bool isVoidElement(String tagName) {
 /// <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-end.html#html-fragment-serialization-algorithm>
 void writeTextNodeAsHtml(StringBuffer str, Text node) {
   // Don't escape text for certain elements, notably <script>.
-  final parent = node.parent;
+  final parent = node.parentNode;
   if (parent is Element) {
     var tag = parent.localName;
     if (rcdataElements.contains(tag) || tag == 'plaintext') {