Delete pop-pop-win from the repo

samples/pop_pop_win/chrome_app/platform_chrome_app.dart

-// Copyright (c) 2014, 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 pop_pop_win.platform_chrome_app;
-
-import 'dart:async';
-
-import 'package:pop_pop_win/platform_target.dart';
-import 'package:chrome/gen/storage.dart';
-
-class PlatformChromeApp extends PlatformTarget {
-  final StreamController _aboutController = new StreamController(sync: true);
-  bool _about = false;
-
-  int get size => 7;
-
-  PlatformChromeApp(): super.base();
-
-  Future clearValues() => storage.local.clear();
-
-  Future setValue(String key, String value) => storage.local.set({key : value});
-
-  Future<String> getValue(String key) => storage.local.get(key)
-        .then((Map<String, String> values) => values[key]);
-
-  bool get showAbout => _about;
-
-  Stream get aboutChanged => _aboutController.stream;
-
-  void toggleAbout([bool value]) {
-    assert(_about != null);
-    if (value == null) {
-      value = !_about;
-    }
-    _about = value;
-    _aboutController.add(null);
-  }
-}