Add unmodifiable list view.

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

Index: tools/dom/templates/html/impl/impl_HTMLSelectElement.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_HTMLSelectElement.darttemplate b/tools/dom/templates/html/impl/impl_HTMLSelectElement.darttemplate
index 0f378abaf9a3e62a6d2f3e1365d69b92e8580859..3417187933995eaca92acb939b1f458e5381c352 100644
--- a/tools/dom/templates/html/impl/impl_HTMLSelectElement.darttemplate
+++ b/tools/dom/templates/html/impl/impl_HTMLSelectElement.darttemplate
@@ -11,16 +11,14 @@ $!MEMBERS
   // does not operate as a List.
   List<OptionElement> get options {
     var options = this.children.where((e) => e is OptionElement).toList();
-    // TODO(floitsch): find better way to create a read-only list view.
-    return options.take(options.length);
+    return new UnmodifiableListView<OptionElement>(options);
   }
 
   List<OptionElement> get selectedOptions {
     // IE does not change the selected flag for single-selection items.
     if (this.multiple) {
       var options = this.options.where((o) => o.selected).toList();
-      // TODO(floitsch): find better way to create a read-only list view.
-      return options.take(options.length);
+      return new UnmodifiableListView<OptionElement>(options);
     } else {
       return [this.options[this.selectedIndex]];
     }