Break up another large file

pkg/analyzer/lib/task/dart.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.dart;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
-import 'package:analyzer/src/generated/error.dart';
+import 'package:analyzer/error/error.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
  * The analysis errors associated with a [Source] representing a compilation
  * unit.
  */
 final ListResultDescriptor<AnalysisError> DART_ERRORS =
@@ skipping 154 matching lines @@
   @override
   bool operator ==(other) {
     return other is LibrarySpecificUnit &&
         other.library == library &&
         other.unit == unit;
   }
 
   @override
   String toString() => '$unit in $library';
 }