pkg/third_party/html5lib: lots of cleanup

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

Index: pkg/third_party/html5lib/lib/src/treebuilder.dart
diff --git a/pkg/third_party/html5lib/lib/src/treebuilder.dart b/pkg/third_party/html5lib/lib/src/treebuilder.dart
index bb53d58509881ed00855f02a284c94e7d19ed296..dd5b994f5751a4c570bf8a78aff55985c38c3df5 100644
--- a/pkg/third_party/html5lib/lib/src/treebuilder.dart
+++ b/pkg/third_party/html5lib/lib/src/treebuilder.dart
@@ -12,7 +12,7 @@ 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.
@@ -24,9 +24,9 @@ class ActiveFormattingElements extends ListProxy<Node> {
   // calling code instead?
   void add(Node node) {
     int equalCount = 0;
-    if (node != Marker) {
+    if (node != MARKER) {
       for (Node element in reversed) {
-        if (element == Marker) {
+        if (element == MARKER) {
           break;
         }
         if (_nodesEqual(element, node)) {
@@ -109,7 +109,7 @@ class TreeBuilder {
     //match any node with that name
     bool exactNode = target is Node && target.nameTuple != null;
 
-    List listElements1 = scopingElements;
+    List listElements1 = SCOPING_ELEMENTS;
     List listElements2 = const [];
     bool invert = false;
     if (variant != null) {
@@ -161,12 +161,12 @@ class TreeBuilder {
     // Step 2 and step 3: we start with the last element. So i is -1.
     int i = activeFormattingElements.length - 1;
     var entry = activeFormattingElements[i];
-    if (entry == Marker || openElements.contains(entry)) {
+    if (entry == MARKER || openElements.contains(entry)) {
       return;
     }
 
     // Step 6
-    while (entry != Marker && !openElements.contains(entry)) {
+    while (entry != MARKER && !openElements.contains(entry)) {
       if (i == 0) {
         //This will be reset to 0 below
         i = -1;
@@ -206,7 +206,7 @@ class TreeBuilder {
 
   void clearActiveFormattingElements() {
     var entry = activeFormattingElements.removeLast();
-    while (activeFormattingElements.length > 0 && entry != Marker) {
+    while (activeFormattingElements.length > 0 && entry != MARKER) {
       entry = activeFormattingElements.removeLast();
     }
   }
@@ -220,7 +220,7 @@ class TreeBuilder {
     for (Node item in activeFormattingElements.reversed) {
       // Check for Marker first because if it's a Marker it doesn't have a
       // name attribute.
-      if (item == Marker) {
+      if (item == MARKER) {
         break;
       } else if (item.tagName == name) {
         return item;
@@ -279,7 +279,7 @@ class TreeBuilder {
   Element insertElementTable(token) {
     /** Create an element and insert it into the tree */
     var element = createElement(token);
-    if (!tableInsertModeElements.contains(openElements.last.tagName)) {
+    if (!TABLE_INSERT_MODE_ELEMENTS.contains(openElements.last.tagName)) {
       return insertElementNormal(token);
     } else {
       // We should be in the InTable mode. This means we want to do
@@ -303,7 +303,7 @@ class TreeBuilder {
     var parent = openElements.last;
 
     if (!insertFromTable || insertFromTable &&
-        !tableInsertModeElements.contains(openElements.last.tagName)) {
+        !TABLE_INSERT_MODE_ELEMENTS.contains(openElements.last.tagName)) {
       _insertText(parent, data, span);
     } else {
       // We should be in the InTable mode. This means we want to do