anchor.diff:  
     for (var typeMirror in jsInterfaceTypes) {
       mirrors.LibraryMirror libraryMirror = typeMirror.owner;
  +    var location = libraryMirror.location;
  +    var dartLibrary = location != null && location.sourceUri.scheme == 'dart';
  +
       var prefixName;
       if (libraryPrefixes.containsKey(libraryMirror)) {
         prefixName = libraryPrefixes[libraryMirror];
  
positive.code:       if (isDom || isJsInterop) {
          // TODO(jacobr): verify class implements JavaScriptObject.
          var className = mirrors.MirrorSystem.getName(clazz.simpleName);
          bool isPrivate = className.startsWith('_');
          var classNameImpl = '${className}Impl';
          var sbPatch = new StringBuffer();
          if (isJsInterop) {
  
negative.code:           sbPatch.write(
                "  static Type get instanceRuntimeType => ${classNameImpl};\n");
          }
          if (isPrivateUserDefinedClass) {
            sb.write("""
  class ${escapePrivateClassPrefix}${className} implements $className {}
  """);
  