Remove AsyncError with Expando.

utils/apidoc/apidoc.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.
 
 /**
  * This generates the reference documentation for the core libraries that come
  * with dart. It is built on top of dartdoc, which is a general-purpose library
  * for generating docs from any Dart code. This library extends that to include
  * additional information and styling specific to our standard library.
  *
@@ skipping 137 matching lines @@
     apidoc.includedLibraries = includedLibraries;
 
     // TODO(amouravski): make apidoc use roughly the same flow as bin/dartdoc.
     Future.wait([copiedStatic, copiedApiDocStatic, htmlDiff])
       .then((_) => apidoc.documentLibraries(apidocLibraries, libPath,
             packageRoot))
       .then((_) => compileScript(mode, outputDir, libPath))
       .then((_) => print(apidoc.status))
       .catchError((e) {
         print('Error: generation failed: ${e}');
+        var trace = getAttachedStackTrace(e);
+        if (trace != null) print("StackTrace: $trace");
         apidoc.cleanup();
         exit(1);
       })
       .whenComplete(() => apidoc.cleanup());
   });
 }
 
 class Apidoc extends Dartdoc {
   /** Big ball of JSON containing the scraped MDN documentation. */
   final Map mdn;
@@ skipping 285 matching lines @@
 /** Converts a local path string to a `file:` [Uri]. */
 Uri _pathToFileUri(String path) {
   path = pathos.absolute(path);
   if (Platform.operatingSystem != 'windows') {
     return Uri.parse('file://$path');
   } else {
     return Uri.parse('file:///${path.replaceAll("\\", "/")}');
   }
 }