Implement getRange (returning an Iterable).

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 bd15590cd7e85bcff2febcaebe65ab189df8f3d5..ed1299ef8454d28ba5977f03eac7626e15730b6f 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -205,14 +205,15 @@ class _ChildrenElementList extends ListBase<Element> {
     throw new UnimplementedError();
   }
 
+  Iterable getRange(int start, int end)  {
+    throw new UnimplementedError();
+  }
+
   List sublist(int start, [int end]) {
     if (end == null) end = length;
     return new _FrozenElementList._wrap(Lists.getRange(this, start, end, []));
   }
 
-  List getRange(int start, int rangeLength) =>
-      sublist(start, start + rangeLength);
-
   int indexOf(Element element, [int start = 0]) {
     return Lists.indexOf(this, element, start, this.length);
   }