Make sure NodeValidator uriAttributes aren't passed as attributes

tools/dom/src/NodeValidatorBuilder.dart

Index: tools/dom/src/NodeValidatorBuilder.dart
diff --git a/tools/dom/src/NodeValidatorBuilder.dart b/tools/dom/src/NodeValidatorBuilder.dart
index 7ebeb36dd1deb3155d531f19be3b2161c10ffd8f..4a412325bd30ba1bf628e02184d54852f7e7a786 100644
--- a/tools/dom/src/NodeValidatorBuilder.dart
+++ b/tools/dom/src/NodeValidatorBuilder.dart
@@ -259,17 +259,17 @@ class NodeValidatorBuilder implements NodeValidator {
 }
 
 class _SimpleNodeValidator implements NodeValidator {
-  final Set<String> allowedElements;
-  final Set<String> allowedAttributes;
-  final Set<String> allowedUriAttributes;
+  final Set<String> allowedElements = new Set<String>();
+  final Set<String> allowedAttributes = new Set<String>();
+  final Set<String> allowedUriAttributes = new Set<String>();
   final UriPolicy uriPolicy;
 
   factory _SimpleNodeValidator.allowNavigation(UriPolicy uriPolicy) {
     return new _SimpleNodeValidator(uriPolicy,
-      allowedElements: [
+      allowedElements: const [
         'A',
         'FORM'],
-      allowedAttributes: [
+      allowedAttributes: const [
         'A::accesskey',
         'A::coords',
         'A::hreflang',
@@ -286,7 +286,7 @@ class _SimpleNodeValidator implements NodeValidator {
         'FORM::novalidate',
         'FORM::target',
       ],
-      allowedUriAttributes: [
+      allowedUriAttributes: const [
         'A::href',
         'FORM::action',
       ]);
@@ -294,10 +294,10 @@ class _SimpleNodeValidator implements NodeValidator {
 
   factory _SimpleNodeValidator.allowImages(UriPolicy uriPolicy) {
     return new _SimpleNodeValidator(uriPolicy,
-      allowedElements: [
+      allowedElements: const [
         'IMG'
       ],
-      allowedAttributes: [
+      allowedAttributes: const [
         'IMG::align',
         'IMG::alt',
         'IMG::border',
@@ -309,14 +309,14 @@ class _SimpleNodeValidator implements NodeValidator {
         'IMG::vspace',
         'IMG::width',
       ],
-      allowedUriAttributes: [
+      allowedUriAttributes: const [
         'IMG::src',
       ]);
   }
 
   factory _SimpleNodeValidator.allowTextElements() {
     return new _SimpleNodeValidator(null,
-      allowedElements: [
+      allowedElements: const [
         'B',
         'BLOCKQUOTE',
         'BR',
@@ -344,13 +344,18 @@ class _SimpleNodeValidator implements NodeValidator {
    */
   _SimpleNodeValidator(this.uriPolicy,
       {Iterable<String> allowedElements, Iterable<String> allowedAttributes,
-      Iterable<String> allowedUriAttributes}):
-      this.allowedElements = allowedElements != null ?
-          new Set.from(allowedElements) : new Set(),
-      this.allowedAttributes = allowedAttributes != null ?
-          new Set.from(allowedAttributes) : new Set(),
-      this.allowedUriAttributes = allowedUriAttributes != null ?
-          new Set.from(allowedUriAttributes) : new Set();
+        Iterable<String> allowedUriAttributes}) {
+    this.allowedElements.addAll(allowedElements ?? const []);
+    allowedAttributes = allowedAttributes ?? const [];
+    allowedUriAttributes = allowedUriAttributes ?? const [];
+    var legalAttributes = allowedAttributes.where(
+        (x) => !_Html5NodeValidator._uriAttributes.contains(x));
+    var extraUriAttributes = allowedAttributes.where(
+        (x) => _Html5NodeValidator._uriAttributes.contains(x));
+    this.allowedAttributes.addAll(legalAttributes);
+    this.allowedUriAttributes.addAll(allowedUriAttributes);
+    this.allowedUriAttributes.addAll(extraUriAttributes);
+  }
 
   bool allowsElement(Element element) {
     return allowedElements.contains(element.tagName);