Update the API documentations with Paul review comments.

pkg/analyzer/lib/src/dart/analysis/file_byte_store.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 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/dart/analysis/byte_store.dart';
 
 /**
  * [ByteStore] that stores values as [File]s.
+ *
+ * TODO(scheglov) Add some eviction policies.
  */
 class FileByteStore implements ByteStore {
   final Folder folder;
 
   FileByteStore(this.folder);
 
   @override
   List<int> get(String key) {
     try {
       File file = folder.getChildAssumingFile(key);
       return file.readAsBytesSync();
     } catch (_) {
       return null;
     }
   }
 
   @override
   void put(String key, List<int> bytes) {
     try {
       File file = folder.getChildAssumingFile(key);
       file.writeAsBytesSync(bytes);
     } catch (_) {}
   }
 }