Simplify _FrozenElementList

tools/dom/templates/html/impl/impl_Element.darttemplate

Index: tools/dom/templates/html/impl/impl_Element.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index 04f51e1e03ab1f3c21c0857454de9de2621df23c..0fe41b01dc0cfcce5b96a9947e736582a0d02eb5 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -253,19 +253,17 @@ abstract class ElementList<T extends Element> extends ListBase<T> {
 $!STREAM_GETTER_SIGNATURES
 }
 
-// TODO(jacobr): this is an inefficient implementation but it is hard to see
-// a better option given that we cannot quite force NodeList to be an
-// ElementList as there are valid cases where a NodeList JavaScript object
-// contains Node objects that are not Elements.
-class _FrozenElementList<T extends Element> extends ListBase<T>
-    implements ElementList<T>, NodeListWrapper {
+// Wrapper over an immutable NodeList to make it implement ElementList.
+//
+// Clients are {`Document`, `DocumentFragment`}.`querySelectorAll` which are
+// declared to return `ElementList`.  This provides all the static analysis
+// benefit so there is no need for this class have a constrained type parameter.
+//
+class _FrozenElementList extends ListBase
+    implements ElementList, NodeListWrapper {
   final List<Node> _nodeList;
-  // The subset of _nodeList that are Elements.
-  List<Element> _elementList;
 
-  _FrozenElementList._wrap(this._nodeList) {
-    _elementList = _nodeList.where((e) => e is Element).toList();
-  }
+  _FrozenElementList._wrap(this._nodeList);
 
   int get length => _nodeList.length;
 
@@ -293,22 +291,22 @@ class _FrozenElementList<T extends Element> extends ListBase<T>
 
   Element get single => _nodeList.single;
 
-  CssClassSet get classes => new _MultiElementCssClassSet(_elementList);
+  CssClassSet get classes => new _MultiElementCssClassSet(this);
 
   CssStyleDeclarationBase get style =>
-      new _CssStyleDeclarationSet(_elementList);
+      new _CssStyleDeclarationSet(this);
 
   void set classes(Iterable<String> value) {
-    _elementList.forEach((e) => e.classes = value);
+    _nodeList.forEach((e) => e.classes = value);
   }
 
-  CssRect get contentEdge => new _ContentCssListRect(_elementList);
+  CssRect get contentEdge => new _ContentCssListRect(this);
 
-  CssRect get paddingEdge => _elementList.first.paddingEdge;
+  CssRect get paddingEdge => this.first.paddingEdge;
 
-  CssRect get borderEdge => _elementList.first.borderEdge;
+  CssRect get borderEdge => this.first.borderEdge;
 
-  CssRect get marginEdge => _elementList.first.marginEdge;
+  CssRect get marginEdge => this.first.marginEdge;
 
   List<Node> get rawList => _nodeList;