Add implementations of the front end FileSystem API.

pkg/front_end/lib/physical_file_system.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.physical_file_system;
+
+import 'dart:async';
+import 'dart:io' as io;
+
+import 'package:path/path.dart' as p;
+
+import 'file_system.dart';
+
+/// Concrete implementation of [FileSystem] which performs its operations using
+/// I/O.
+///
+/// Not intended to be implemented or extended by clients.
+class PhysicalFileSystem implements FileSystem {
+  static PhysicalFileSystem instance = new PhysicalFileSystem._();

[scheglov, 2016/11/03 02:15:24]

+final?

[Paul Berry, 2016/11/03 15:16:41]

Done.  Thank you.

+
+  PhysicalFileSystem._();
+
+  @override
+  p.Context get context => p.context;
+
+  @override
+  FileSystemEntity entityForPath(String path) =>
+      new _PhysicalFileSystemEntity(context.normalize(context.absolute(path)));
+
+  @override
+  FileSystemEntity entityForUri(Uri uri) {
+    if (uri.scheme != 'file') throw new ArgumentError('File URI expected');
+    return entityForPath(context.fromUri(uri));
+  }
+}
+
+/// Concrete implementation of [FileSystemEntity] for use by
+/// [PhysicalFileSystem].
+class _PhysicalFileSystemEntity implements FileSystemEntity {
+  @override
+  final String path;
+
+  _PhysicalFileSystemEntity(this.path);
+
+  @override
+  int get hashCode => path.hashCode;
+
+  @override
+  bool operator ==(Object other) =>
+      other is _PhysicalFileSystemEntity && other.path == path;
+
+  @override
+  Future<List<int>> readAsBytes() => new io.File(path).readAsBytes();
+
+  @override
+  Future<String> readAsString() => new io.File(path).readAsString();
+}