Fix apidoc to work with latest frog and dartdoc.

utils/apidoc/apidoc.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Generates the complete set of corelib reference documentation.
  */
 #library('apidoc');
 
 #import('html_diff.dart');
@@ skipping 142 matching lines @@
     return "";
   }
 }
 
 /**
  * Returns additional Markdown-formatted documentation for [type], linking it to
  * the corresponding `dart:html` or `dart:dom` [Type](s). If [type] is not in
  * `dart:html` or `dart:dom`, returns no additional documentation.
  */
 String getTypeDoc(Type type) {
-  if (_diff.domTypesToHtml.containsKey(type)) {
-    var htmlTypes = doc.joinWithCommas(
-        map(_diff.domTypesToHtml[type], _linkType));
-    return "_This corresponds to $htmlTypes in the [dart:html](../html.html) " +
-      "library._";
-  } else if (_diff.htmlTypesToDom.containsKey(type)) {
-    var domTypes = doc.joinWithCommas(
-        map(_diff.htmlTypesToDom[type], _linkType));
-    return "_This corresponds to $domTypes in the [dart:dom](../dom.html) " +
-      "library._";
-  } else {
-    return "";
+  var types = _diff.domTypesToHtml[type];
+  if (types != null && types.length > 0) {
+    final text = doc.joinWithCommas(map(types, _linkType));
+    return '_This corresponds to $text in the [dart:html](../html.html) ' +
+      'library._';
   }
+
+  types = _diff.htmlTypesToDom[type];
+  if (types != null && types.length > 0) {
+    final text = doc.joinWithCommas(map(types, _linkType));
+    return '_This corresponds to $text in the [dart:dom](../dom.html) ' +
+      'library._';
+  }
+
+  return '';
 }