Break up another large file

pkg/analyzer/lib/src/task/yaml.dart

 // Copyright (c) 2016, 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 analyzer.src.task.yaml;
 
+import 'package:analyzer/error/error.dart';
 import 'package:analyzer/exception/exception.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/dart/scanner/scanner.dart';
 import 'package:analyzer/src/generated/engine.dart';
-import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/task/general.dart';
 import 'package:analyzer/task/general.dart';
 import 'package:analyzer/task/model.dart';
 import 'package:analyzer/task/yaml.dart';
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
 
 /**
  * A task that scans the content of a YAML file, producing a YAML document.
@@ skipping 124 matching lines @@
    */
   const YamlErrorCode(String name, String message, [String correction])
       : super(name, message, correction);
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.ERROR;
 
   @override
   ErrorType get type => ErrorType.COMPILE_TIME_ERROR;
 }