Delete the example conditional screen (#8730)

* Delete the example conditional screen

* fix dart doc

packages/devtools_app/lib/src/app.dart

diff --git a/packages/devtools_app/lib/src/app.dart b/packages/devtools_app/lib/src/app.dart
index cd7e737..c09266d 100644
--- a/packages/devtools_app/lib/src/app.dart
+++ b/packages/devtools_app/lib/src/app.dart
@@ -12,7 +12,6 @@
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
-import 'example/conditional_screen.dart';
 import 'extensions/extension_screen.dart';
 import 'framework/disconnect_observer.dart';
 import 'framework/framework_core.dart';
@@ -59,10 +58,6 @@
 import 'shared/utils/utils.dart';
 import 'standalone_ui/standalone_screen.dart';
 
-// Assign to true to use a sample implementation of a conditional screen.
-// WARNING: Do not check in this file if debugEnableSampleScreen is true.
-const debugEnableSampleScreen = false;
-
 /// Top-level configuration for the app.
 @immutable
 class DevToolsApp extends StatefulWidget {
@@ -684,12 +679,6 @@
       VMDeveloperToolsScreen(),
       createController: (_) => VMDeveloperToolsController(),
     ),
-    // Show the sample DevTools screen.
-    if (debugEnableSampleScreen && (kDebugMode || kProfileMode))
-      DevToolsScreen<ExampleController>(
-        const ExampleConditionalScreen(),
-        createController: (_) => ExampleController(),
-      ),
   ];
 }
 

packages/devtools_app/lib/src/example/conditional_screen.dart

diff --git a/packages/devtools_app/lib/src/example/conditional_screen.dart b/packages/devtools_app/lib/src/example/conditional_screen.dart
deleted file mode 100644
index d68009f..0000000
--- a/packages/devtools_app/lib/src/example/conditional_screen.dart
+++ /dev/null
@@ -1,127 +0,0 @@
-// Copyright 2020 The Flutter Authors
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file or at https://developers.google.com/open-source/licenses/bsd.
-
-import 'dart:async';
-
-import 'package:devtools_app_shared/utils.dart';
-import 'package:flutter/material.dart';
-
-import '../shared/framework/screen.dart';
-import '../shared/globals.dart';
-import '../shared/offline/offline_data.dart';
-import '../shared/utils/utils.dart';
-
-/// This is an example implementation of a conditional screen that supports
-/// offline mode and uses a provided controller [ExampleController].
-///
-/// This class exists solely as an example and should not be used in the
-/// DevTools app.
-class ExampleConditionalScreen extends Screen {
-  const ExampleConditionalScreen()
-    : super.conditional(
-        id: id,
-        requiresLibrary: 'package:flutter/',
-        title: 'Example',
-        icon: Icons.palette,
-        worksWithOfflineData: true,
-      );
-
-  static const id = 'example';
-
-  @override
-  Widget buildScreenBody(BuildContext context) {
-    return const _ExampleConditionalScreenBody();
-  }
-}
-
-class _ExampleConditionalScreenBody extends StatefulWidget {
-  const _ExampleConditionalScreenBody();
-
-  @override
-  _ExampleConditionalScreenBodyState createState() =>
-      _ExampleConditionalScreenBodyState();
-}
-
-class _ExampleConditionalScreenBodyState
-    extends State<_ExampleConditionalScreenBody>
-    with
-        ProvidedControllerMixin<
-          ExampleController,
-          _ExampleConditionalScreenBody
-        > {
-  @override
-  void didChangeDependencies() {
-    super.didChangeDependencies();
-    initController();
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return ValueListenableBuilder<ExampleScreenData>(
-      valueListenable: controller.data,
-      builder: (context, data, _) {
-        return Center(child: Text(data.title));
-      },
-    );
-  }
-}
-
-class ExampleController extends DisposableController
-    with
-        AutoDisposeControllerMixin,
-        OfflineScreenControllerMixin<ExampleScreenData> {
-  ExampleController() {
-    unawaited(_init());
-  }
-
-  final data = ValueNotifier<ExampleScreenData>(
-    ExampleScreenData('Example screen'),
-  );
-
-  final _initialized = Completer<void>();
-
-  Future<void> get initialized => _initialized.future;
-
-  Future<void> _init() async {
-    await _initHelper();
-    _initialized.complete();
-  }
-
-  Future<void> _initHelper() async {
-    if (!offlineDataController.showingOfflineData.value) {
-      // Do some initialization for online mode.
-    } else {
-      await maybeLoadOfflineData(
-        ExampleConditionalScreen.id,
-        createData: (json) => ExampleScreenData.fromJson(json),
-        shouldLoad: (data) => data.title.isNotEmpty,
-        loadData: (data) => this.data.value = data,
-      );
-    }
-  }
-
-  // Overrides for [OfflineScreenControllerMixin]
-
-  @override
-  OfflineScreenData prepareOfflineScreenData() {
-    return OfflineScreenData(
-      screenId: ExampleConditionalScreen.id,
-      data: data.value.json,
-    );
-  }
-}
-
-class ExampleScreenData {
-  ExampleScreenData(this.title);
-
-  factory ExampleScreenData.fromJson(Map<String, Object?> json) {
-    return ExampleScreenData(json[_titleKey] as String);
-  }
-
-  static const _titleKey = 'title';
-
-  final String title;
-
-  Map<String, Object?> get json => {_titleKey: title};
-}

packages/devtools_app/lib/src/shared/framework/screen.dart

diff --git a/packages/devtools_app/lib/src/shared/framework/screen.dart b/packages/devtools_app/lib/src/shared/framework/screen.dart
index e43b1af..a30d7f1 100644
--- a/packages/devtools_app/lib/src/shared/framework/screen.dart
+++ b/packages/devtools_app/lib/src/shared/framework/screen.dart
@@ -156,14 +156,12 @@
   }
 }
 
-/// Defines a page shown in the DevTools [TabBar].
+/// Defines a screen shown in the top-level DevTools [TabBar].
 ///
-/// A devtools screen can be in three modes:
-/// * offline-data
-/// * connected
-/// * not-connected
-///
-/// See [devToolsMode].
+/// A DevTools screen can be in three modes:
+/// * showing offline-data
+/// * connected to an application
+/// * not connected to an application
 ///
 /// A screen may support any combination of modes.
 ///