Make IndexableObjectKind parameterized.

pkg/analysis_server/lib/src/services/index/indexable_file.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 services.index.indexable_file;
 
 import 'package:analysis_server/plugin/index/index_core.dart';
 import 'package:analyzer/src/generated/engine.dart';
 
 /**
@@ skipping 24 matching lines @@
   bool operator ==(Object object) =>
       object is IndexableFile && object.path == path;
 
   @override
   String toString() => path;
 }
 
 /**
  * The kind of an indexable file.
  */
-class IndexableFileKind implements IndexableObjectKind {
+class IndexableFileKind implements IndexableObjectKind<IndexableFile> {
   /**
    * The unique instance of this class.
    */
   static final IndexableFileKind INSTANCE =
       new IndexableFileKind._(IndexableObjectKind.nextIndex);
 
   /**
    * The index uniquely identifying this kind.
    */
   final int index;
 
   /**
    * Initialize a newly created kind to have the given [index].
    */
   IndexableFileKind._(this.index) {
     IndexableObjectKind.register(this);
   }
 
   @override
-  IndexableObject decode(AnalysisContext context, String filePath, int offset) {
+  IndexableFile decode(AnalysisContext context, String filePath, int offset) {
     return new IndexableFile(filePath);
   }
 
   @override
-  int encodeHash(StringToInt stringToInt, IndexableObject indexable) {
-    String path = (indexable as IndexableFile).path;
+  int encodeHash(StringToInt stringToInt, IndexableFile indexable) {
+    String path = indexable.path;
     return stringToInt(path);
   }
 }