Create new error message for missing generated files

pkg/analysis_server/lib/src/services/correction/fix.dart

 // Copyright (c) 2014, 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.
 
 library analysis_server.src.services.correction.fix;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/edit/fix/fix_core.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
@@ skipping 62 matching lines @@
     errorCode == StaticWarningCode.FUNCTION_WITHOUT_CALL ||
     errorCode == StaticWarningCode.UNDEFINED_IDENTIFIER ||
     errorCode ==
         CompileTimeErrorCode.CONST_INITIALIZED_WITH_NON_CONSTANT_VALUE ||
     errorCode == CompileTimeErrorCode.INVALID_ANNOTATION ||
     errorCode == CompileTimeErrorCode.NO_DEFAULT_SUPER_CONSTRUCTOR_EXPLICIT ||
     errorCode == CompileTimeErrorCode.PART_OF_NON_PART ||
     errorCode ==
         CompileTimeErrorCode.UNDEFINED_CONSTRUCTOR_IN_INITIALIZER_DEFAULT ||
     errorCode == CompileTimeErrorCode.URI_DOES_NOT_EXIST ||
+    errorCode == CompileTimeErrorCode.URI_HAS_NOT_BEEN_GENERATED ||
     errorCode == HintCode.CAN_BE_NULL_AFTER_NULL_AWARE ||
     errorCode == HintCode.DEAD_CODE ||
     errorCode == HintCode.DIVISION_OPTIMIZATION ||
     errorCode == HintCode.TYPE_CHECK_IS_NOT_NULL ||
     errorCode == HintCode.TYPE_CHECK_IS_NULL ||
     errorCode == HintCode.UNDEFINED_GETTER ||
     errorCode == HintCode.UNDEFINED_SETTER ||
     errorCode == HintCode.UNNECESSARY_CAST ||
     errorCode == HintCode.UNUSED_CATCH_CLAUSE ||
     errorCode == HintCode.UNUSED_CATCH_STACK ||
@@ skipping 140 matching lines @@
   @override
   final AnalysisError error;
 
   FixContextImpl(this.resourceProvider, this.analysisContext, this.error);
 
   FixContextImpl.from(FixContext other)
       : resourceProvider = other.resourceProvider,
         analysisContext = other.analysisContext,
         error = other.error;
 }