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

pkg/analyzer/test/src/dart/analysis/file_state_test.dart

Index: pkg/analyzer/test/src/dart/analysis/file_state_test.dart
diff --git a/pkg/analyzer/test/src/dart/analysis/file_state_test.dart b/pkg/analyzer/test/src/dart/analysis/file_state_test.dart
index b409d92a4d8885ac65b32b5480bda61eb491727b..c58b53b8f949466fbfa3820448bcb11f58f8f75c 100644
--- a/pkg/analyzer/test/src/dart/analysis/file_state_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/file_state_test.dart
@@ -17,7 +17,7 @@ import 'package:analyzer/src/generated/source.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.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:mockito/mockito.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';