Remove AsyncError with Expando.

sdk/lib/_internal/compiler/implementation/compiler.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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 1257 matching lines @@
 }
 
 /// A sink that drains into /dev/null.
 class NullSink implements EventSink<String> {
   final String name;
 
   NullSink(this.name);
 
   add(String value) {}
 
-  void addError(AsyncError error) {}
+  void addError(Object error) {}
 
   void close() {}
 
   toString() => name;
 
   /// Convenience method for getting an [api.CompilerOutputProvider].
   static NullSink outputProvider(String name, String extension) {
     return new NullSink('$name.$extension');
   }
 }