Break up another large file

pkg/analyzer/lib/src/task/html_work_manager.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.src.task.html_work_manager;
 
 import 'dart:collection';
 
+import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/generated/engine.dart'
     show AnalysisEngine, AnalysisErrorInfo, CacheState, InternalAnalysisContext;
-import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_collection.dart';
 import 'package:analyzer/src/task/html.dart';
 import 'package:analyzer/task/html.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
  * The manager for HTML specific analysis.
  */
 class HtmlWorkManager implements WorkManager {
@@ skipping 220 matching lines @@
     return state != CacheState.VALID && state != CacheState.ERROR;
   }
 
   /**
    * Return `true` if the given target is an HTML source.
    */
   static bool _isHtmlSource(AnalysisTarget target) {
     return target is Source && AnalysisEngine.isHtmlFileName(target.fullName);
   }
 }