Revert "Removed local_storage conditional import"

This reverts commit c952120.

pkgs/dartpad_ui/lib/editor/editor.dart

@@ -183,8 +183,7 @@ class _EditorWidgetState extends State<EditorWidget> implements EditorService {
   }
 
   Timer? _autosaveTimer;
-  void _autosave([Timer? _]) {
-    // (Callbacks to [Timer.periodic] must accept a Timer argument)
+  void _autosave([Timer? timer]) {
     final content = widget.appModel.sourceCodeController.text;
     if (content.isEmpty) return;
     LocalStorage.instance.saveUserCode(content);

pkgs/dartpad_ui/lib/local_storage.dart

@@ -2,18 +2,12 @@
 // 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 'package:web/web.dart' as web;
+import 'local_storage/stub.dart'
+    if (dart.library.js_util) 'local_storage/web.dart';
 
-import '../utils.dart';
+abstract class LocalStorage {
+  static LocalStorage instance = LocalStorageImpl();
 
-const _userInputKey = 'user_';
-
-class LocalStorage {
-  static final instance = LocalStorage();
-
-  void saveUserCode(String code) =>
-      web.window.localStorage.setItem(_userInputKey, code);
-
-  String? getUserCode() =>
-      web.window.localStorage.getItem(_userInputKey)?.nullIfEmpty;
+  void saveUserCode(String code);
+  String? getUserCode();
 }

pkgs/dartpad_ui/lib/local_storage/stub.dart

@@ -0,0 +1,16 @@
+// Copyright (c) 2024, 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 '../local_storage.dart';
+import '../utils.dart';
+
+class LocalStorageImpl extends LocalStorage {
+  String? _code;
+
+  @override
+  void saveUserCode(String code) => _code = code;
+
+  @override
+  String? getUserCode() => _code?.nullIfEmpty;
+}

pkgs/dartpad_ui/lib/local_storage/web.dart

@@ -0,0 +1,20 @@
+// Copyright (c) 2024, 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 'package:web/web.dart' as web;
+
+import '../local_storage.dart';
+import '../utils.dart';
+
+const _userInputKey = 'user_';
+
+class LocalStorageImpl extends LocalStorage {
+  @override
+  void saveUserCode(String code) =>
+      web.window.localStorage.setItem(_userInputKey, code);
+
+  @override
+  String? getUserCode() =>
+      web.window.localStorage.getItem(_userInputKey)?.nullIfEmpty;
+}

pkgs/dartpad_ui/test/autosave_test.dart

@@ -17,7 +17,7 @@ Never throwingFallback() =>
 
 void main() {
   const channel = Channel.stable;
-  group('Autosave', () {
+  group('Autosave:', () {
     test('empty content is treated as null', () {
       expect(''.nullIfEmpty, isNull);