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() {
+  }
+
+  var appendChild = 123;

[floitsch, 2015/02/04 00:10:12]

Add small comment so that it is clear that this is the thing that could trip the
compiler.

[asgerf, 2015/02/06 12:15:18]

Done.

+}
+
+main() {
+  document.registerElement('x-custom', CustomElement);
+  CustomElement custom = new CustomElement();
+  document.body.children.add(custom);
+  custom.children.add(new DivElement()..text = 'Hello world!'); // Will call appendChild in JS.

[floitsch, 2015/02/04 00:10:12]

Long line.

[asgerf, 2015/02/06 12:15:18]

I was under the impression that tests were exempt from that rule. But fixed
anyway.

+}