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

pkg/front_end/lib/compiler_options.dart

 // Copyright (c) 2016, 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 front_end.compiler_options;
 
 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:kernel/target/targets.dart' show Target;
 
 import 'compilation_message.dart';
 import 'file_system.dart';
 import 'physical_file_system.dart';
 
 /// Callback used to report errors encountered during compilation.
 typedef void ErrorHandler(CompilationMessage error);
 
 /// Front-end options relevant to compiler back ends.
@@ skipping 206 matching lines @@
   ///
   /// Typically used by developers to debug internals of the compiler.
   bool throwOnWarnings = false;
 
   /// Whether the compiler should throw as soon as it encounters a
   /// compilation nit.
   ///
   /// Typically used by developers to debug internals of the compiler.
   bool throwOnNits = false;
 }