Revert "dart2js: Refactoring, documentation, and a few bugfixes in Namer class."

tests/html/custom_element_name_clash_test.dart

-// Copyright (c) 2015, 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.
-
-library custom_elements_name_clash;
-
-import 'dart:html';
-
-class CustomElement extends HtmlElement {
-  factory CustomElement() => new Element.tag('x-custom');
-
-  CustomElement.created() : super.created() {
-  }
-
-  // Try to clash with native 'appendChild' method.
-  var appendChild = 123;
-}
-
-main() {
-  document.registerElement('x-custom', CustomElement);
-  CustomElement custom = new CustomElement();
-  document.body.children.add(custom);
-  // Will call appendChild in JS.
-  custom.children.add(new DivElement()..text = 'Hello world!'); 
-}