Move _HTMLElement to HtmlElement

tools/dom/templates/html/dart2js/html_dart2js.darttemplate

Index: tools/dom/templates/html/dart2js/html_dart2js.darttemplate
diff --git a/tools/dom/templates/html/dart2js/html_dart2js.darttemplate b/tools/dom/templates/html/dart2js/html_dart2js.darttemplate
index 2753cb843a123f9b94beb5fa3394da30ce3dd026..62fcb2810b9b6ab7a6b004a8d6a8835fdc97b466 100644
--- a/tools/dom/templates/html/dart2js/html_dart2js.darttemplate
+++ b/tools/dom/templates/html/dart2js/html_dart2js.darttemplate
@@ -94,8 +94,8 @@ ElementList queryAll(String selector) => document.queryAll(selector);
 
 // Workaround for tags like <cite> that lack their own Element subclass --
 // Dart issue 1990.
-class _HTMLElement extends Element native "HTMLElement" {
-  factory _HTMLElement() { throw new UnsupportedError("Not supported"); }
+class HtmlElement extends Element native "HTMLElement" {
+  factory HtmlElement() { throw new UnsupportedError("Not supported"); }
 }
 
 // Support for Send/ReceivePortSync.