Add support code to make fixes easier in plugins

pkg/analysis_server/lib/plugin/edit/fix/fix_core.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.
 
 import 'dart:async';
 
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart'
     show SourceChange;
+import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 
 /**
  * A description of a single proposed fix for some problem.
  *
  * Clients may not extend, implement or mix-in this class.
  */
 class Fix {
   /**
    * An empty list of fixes.
    */
   static const List<Fix> EMPTY_LIST = const <Fix>[];
 
   /**
    * A comparator that can be used to sort fixes by their relevance. The most
    * relevant fixes will be sorted before fixes with a lower relevance.
    */
   static final Comparator<Fix> SORT_BY_RELEVANCE =
       (Fix firstFix, Fix secondFix) =>
-          firstFix.kind.relevance - secondFix.kind.relevance;
+          firstFix.kind.priority - secondFix.kind.priority;
 
   /**
    * A description of the fix being proposed.
    */
   final FixKind kind;
 
   /**
    * The change to be made in order to apply the fix.
    */
   final SourceChange change;
@@ skipping 37 matching lines @@
  * [computeFixes].
  *
  * Clients may implement this class when implementing plugins.
  */
 abstract class FixContributor {
   /**
    * Return a list of fixes for the given [context].
    */
   Future<List<Fix>> computeFixes(FixContext context);
 }
-
-/**
- * A description of a class of fixes. Instances are intended to hold the
- * information that is common across a number of fixes and to be shared by those
- * fixes. For example, if an unnecessary cast is found then one of the suggested
- * fixes will be to remove the cast. If there are multiple unnecessary casts in
- * a single file, then there will be multiple fixes, one per occurrence, but
- * they will all share the same kind.
- *
- * Clients may not extend, implement or mix-in this class.
- */
-class FixKind {
-  /**
-   * The name of this kind of fix, used for debugging.
-   */
-  final String name;
-
-  /**
-   * The relevance of this kind of fix for the kind of error being addressed.
-   */
-  final int relevance;
-
-  /**
-   * A human-readable description of the changes that will be applied by this
-   * kind of fix.
-   */
-  final String message;
-
-  /**
-   * Initialize a newly created kind of fix to have the given [name],
-   * [relevance] and [message].
-   */
-  const FixKind(this.name, this.relevance, this.message);
-
-  @override
-  String toString() => name;
-}