Add attribute information table so we generate correct setters.

lib/src/html5_utils.dart

 // Copyright (c) 2012, 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.
 
 // TODO(jmesserly): html5lib might be a better home for this.
 // But at the moment we only need it here.
 
 library html5_utils;
 
+
+/**
+ * Maps an HTML tag to a dart:html type. This uses [htmlElementNames] but it
+ * will return UnknownElement if the tag is unknown.
+ */
+String typeForHtmlTag(String tag) {
+  var type = htmlElementNames[tag];
+  // Note: this will eventually be the component's class name if it is a
+  // known x-tag.
+  return type == null ? 'UnknownElement' : type;
+}
+
 /**
  * HTML element to DOM type mapping. Source:
  * <http://dev.w3.org/html5/spec/section-index.html#element-interfaces>
  *
  * The 'HTML' prefix has been removed to match `dart:html`, as per:
  * <http://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/lib/html/scripts/htmlrenamer.py>
  * It does not appear any element types are being renamed other than the prefix.
  * However there does not appear to be the last subtypes for the following tags:
  * command, data, dialog, td, th, and time.
  */
@@ skipping 102 matching lines @@
   'time': 'Element', // see doc comment, was: 'TimeElement'
   'title': 'TitleElement',
   'tr': 'TableRowElement',
   'track': 'TrackElement',
   'u': 'Element',
   'ul': 'UListElement',
   'var': 'Element',
   'video': 'VideoElement',
   'wbr': 'Element',
 };