Move byte_store.dart and file_byte_store.dart to their own subdirectory.

pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart

Index: pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart
diff --git a/pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart b/pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart
index 1315741a2e684616f19c63e7d62342e1d9f13c08..0849ca5fe81e87856b68290e6328d61cc1d69243 100644
--- a/pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart
+++ b/pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart
@@ -18,7 +18,7 @@ import 'package:analyzer/src/dart/analysis/session.dart';
 import 'package:analyzer/src/generated/engine.dart' show AnalysisOptionsImpl;
 import 'package:analyzer/src/generated/source.dart';
 import 'package:front_end/src/base/performace_logger.dart';
-import 'package:front_end/src/incremental/byte_store.dart';
+import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';