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

pkg/front_end/lib/src/base/processed_options.dart

 // Copyright (c) 2017, 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 'dart:async';
 
 import 'package:front_end/compilation_message.dart';
 import 'package:front_end/compiler_options.dart';
 import 'package:front_end/file_system.dart';
 import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/fasta/fasta_codes.dart';
 import 'package:front_end/src/fasta/problems.dart' show unimplemented;
 import 'package:front_end/src/fasta/severity.dart';
 import 'package:front_end/src/fasta/ticker.dart';
 import 'package:front_end/src/fasta/uri_translator.dart';
 import 'package:front_end/src/fasta/uri_translator_impl.dart';
-import 'package:front_end/src/incremental/byte_store.dart';
+import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:front_end/src/multi_root_file_system.dart';
 import 'package:kernel/kernel.dart'
     show Program, loadProgramFromBytes, CanonicalName;
 import 'package:kernel/target/targets.dart';
 import 'package:kernel/target/vm_fasta.dart';
 import 'package:package_config/packages.dart' show Packages;
 import 'package:package_config/src/packages_impl.dart'
     show NonFilePackagesDirectoryPackages, MapPackages;
 import 'package:package_config/packages_file.dart' as package_config;
 import 'package:source_span/source_span.dart' show SourceSpan, SourceLocation;
@@ skipping 574 matching lines @@
   String get dart2jsCode => _original.code.dart2jsCode;
 
   SourceSpan get span =>
       new SourceLocation(_original.charOffset, sourceUrl: _original.uri)
           .pointSpan();
 
   _CompilationMessage(this._original, this.severity);
 
   String toString() => message;
 }