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

pkg/analyzer/test/src/task/strong/strong_test_helper.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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 library analyzer.test.src.task.strong.strong_test_helper;
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_resolution_map.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/error/error.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/error_processor.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
 import 'package:analyzer/src/dart/analysis/file_state.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
 import 'package:analyzer/src/error/codes.dart';
 import 'package:analyzer/src/generated/engine.dart';
 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:source_span/source_span.dart';
 import 'package:test/test.dart';
 
 import '../../context/mock_sdk.dart';
 
 SourceSpanWithContext _createSpanHelper(
     LineInfo lineInfo, int start, Source source, String content,
     {int end}) {
   var startLoc = _locationForOffset(lineInfo, source.uri, start);
   var endLoc = _locationForOffset(lineInfo, source.uri, end ?? start);
@@ skipping 447 matching lines @@
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (uri.scheme == 'package') {
       return (provider.getResource(
               provider.convertPath('/packages/' + uri.path)) as File)
           .createSource(uri);
     }
     return super.resolveAbsolute(uri, actualUri);
   }
 }