Simplify _FrozenElementList

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of $LIBRARYNAME;
 
 class _ChildrenElementList extends ListBase<Element>
     implements NodeListWrapper {
   // Raw Element.
   final Element _element;
@@ skipping 235 matching lines @@
    * in this element, in pixels, regardless of this element's box-sizing
    * property. Unlike [getBoundingClientRect], the dimensions of this rectangle
    * will return the same numerical height if the element is hidden or not. This
    * can be used to retrieve jQuery's `outerHeight` value for an element.
    */
   @Experimental()
   CssRect get marginEdge;
 $!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;
 
   Element operator [](int index) => _nodeList[index];
 
   void operator []=(int index, Element value) {
     throw new UnsupportedError('Cannot modify list');
   }
 
   void set length(int newLength) {
     throw new UnsupportedError('Cannot modify list');
   }
 
   void sort([Comparator<Element> compare]) {
     throw new UnsupportedError('Cannot sort list');
   }
 
   void shuffle([Random random]) {
     throw new UnsupportedError('Cannot shuffle list');
   }
 
   Element get first => _nodeList.first;
 
   Element get last => _nodeList.last;
 
   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;
 
 $!ELEMENT_STREAM_GETTERS
 }
 
 @DocsEditable()
 $(ANNOTATIONS)$(NATIVESPEC)abstract class $CLASSNAME$EXTENDS$IMPLEMENTS {
 
   /**
@@ skipping 1160 matching lines @@
   const ScrollAlignment._internal(this._value);
   toString() => 'ScrollAlignment.$_value';
 
   /// Attempt to align the element to the top of the scrollable area.
   static const TOP = const ScrollAlignment._internal('TOP');
   /// Attempt to center the element in the scrollable area.
   static const CENTER = const ScrollAlignment._internal('CENTER');
   /// Attempt to align the element to the bottom of the scrollable area.
   static const BOTTOM = const ScrollAlignment._internal('BOTTOM');
 }