Add support code to make fixes easier in plugins

pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart

Index: pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
diff --git a/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart b/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
index 02b0a2d727e7916176e3638d53ff2f983596eec2..91a813f8214fd13445d3e5db5a79b522a096c6b1 100644
--- a/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
+++ b/pkg/analysis_server/lib/plugin/edit/fix/fix_core.dart
@@ -9,6 +9,7 @@ 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.
@@ -27,7 +28,7 @@ class Fix {
    */
   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.
@@ -85,40 +86,3 @@ abstract class FixContributor {
    */
   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;
-}