pkg/third_party/html5lib: lots of cleanup

pkg/third_party/html5lib/lib/src/treebuilder.dart

 /** Internals to the tree builders. */
 library treebuilder;
 
 import 'dart:collection';
 import 'package:html5lib/dom.dart';
 import 'package:source_maps/span.dart' show FileSpan;
 import 'constants.dart';
 import 'list_proxy.dart';
 import 'token.dart';
 import 'utils.dart';
 
 // The scope markers are inserted when entering object elements,
 // marquees, table cells, and table captions, and are used to prevent formatting
 // from "leaking" into tables, object elements, and marquees.
-final Node Marker = null;
+const Node Marker = null;
 
 // TODO(jmesserly): this should extend ListBase<Node>, but my simple attempt
 // didn't work.
 class ActiveFormattingElements extends ListProxy<Node> {
   ActiveFormattingElements() : super();
 
   // Override the "add" method.
   // TODO(jmesserly): I'd rather not override this; can we do this in the
   // calling code instead?
   void add(Node node) {
@@ skipping 97 matching lines @@
           break;
         case "table":
           listElements1 = const [const Pair(Namespaces.html, "html"),
                                  const Pair(Namespaces.html, "table")];
           break;
         case "select":
           listElements1 = const [const Pair(Namespaces.html, "optgroup"),
                                  const Pair(Namespaces.html, "option")];
           invert = true;
           break;
-        default: assert(false); break;
+        default:
+          throw new StateError('We should never reach this point');
       }
     }
 
     for (Node node in openElements.reversed) {
       if (node.tagName == target && !exactNode ||
           node == target && exactNode) {
         return true;
       } else if (invert !=
           (listElements1.contains(node.nameTuple) ||
            listElements2.contains(node.nameTuple))) {
         return false;
       }
     }
 
-    assert(false); // We should never reach this point
+    throw new StateError('We should never reach this point');
   }
 
   void reconstructActiveFormattingElements() {
     // Within this algorithm the order of steps described in the
     // specification is not quite the same as the order of steps in the
     // code. It should still do the same though.
 
     // Step 1: stop the algorithm when there's nothing to do.
     if (activeFormattingElements.length == 0) {
       return;
@@ skipping 232 matching lines @@
   Document getDocument() => document;
 
   /** Return the final fragment. */
   DocumentFragment getFragment() {
     //XXX assert innerHTML
     var fragment = new DocumentFragment();
     openElements[0].reparentChildren(fragment);
     return fragment;
   }
 }