Break up another large file

pkg/analyzer/lib/task/html.dart

 // Copyright (c) 2015, 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.task.html;
 
-import 'package:analyzer/src/generated/error.dart';
+import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/task/model.dart';
 import 'package:html/dom.dart';
 
 /**
  * The result of parsing an HTML file.
  */
 final ResultDescriptor<Document> HTML_DOCUMENT =
     new ResultDescriptor<Document>('HTML_DOCUMENT', null);
 
 /**
  * The analysis errors associated with a [Source] representing an HTML file.
  */
 final ListResultDescriptor<AnalysisError> HTML_ERRORS =
     new ListResultDescriptor<AnalysisError>(
         'HTML_ERRORS', AnalysisError.NO_ERRORS);
 
 /**
  * The sources of the Dart libraries referenced by an HTML file.
  */
 final ListResultDescriptor<Source> REFERENCED_LIBRARIES =
     new ListResultDescriptor<Source>('REFERENCED_LIBRARIES', Source.EMPTY_LIST);