samples/poppopwin: upgrade to first-class sample

samples/third_party/pop-pop-win/web/platform_web.dart

-library ppw_platform_web;
-
-import 'dart:async';
-import 'dart:html';
-import 'dart:js' as js;
-import 'package:poppopwin/platform_target.dart';
-
-class PlatformWeb extends PlatformTarget {
-  static const String _BIG_HASH = '#big';
-  static const String _ABOUT_HASH = '#about';
-
-  final StreamController _aboutController = new StreamController(sync: true);
-
-  PlatformWeb() : super.base() {
-    window.onPopState.listen((args) => _processUrlHash());
-  }
-
-  @override
-  Future clearValues() {
-    window.localStorage.clear();
-    return new Future.value();
-  }
-
-  @override
-  Future setValue(String key, String value) {
-    window.localStorage[key] = value;
-    return new Future.value();
-  }
-
-  @override
-  Future<String> getValue(String key) =>
-      new Future.value(window.localStorage[key]);
-
-  @override
-  void trackAnalyticsEvent(String category, String action, [String label,
-                                                            int value]) {
-    var args = ['send', 'event', category, action];
-    if(label != null) {
-      args.add(label);
-    }
-
-    if(value != null) {
-      assert(label != null);
-      args.add(value);
-    }
-
-    js.context.callMethod('ga', args);
-  }
-
-  bool get renderBig => _urlHash == _BIG_HASH;
-
-  bool get showAbout => _urlHash == _ABOUT_HASH;
-
-  Stream get aboutChanged => _aboutController.stream;
-
-  void toggleAbout([bool value]) {
-    final Location loc = window.location;
-    // ensure we treat empty hash like '#', which makes comparison easy later
-    final hash = loc.hash.length == 0 ? '#' : loc.hash;
-
-    final isOpen = hash == _ABOUT_HASH;
-    if(value == null) {
-      // then toggle the current value
-      value = !isOpen;
-    }
-
-    var targetHash = value ? _ABOUT_HASH : '#';
-    if(targetHash != hash) {
-      loc.assign(targetHash);
-    }
-    _aboutController.add(null);
-  }
-
-  String get _urlHash => window.location.hash;
-
-  void _processUrlHash() {
-    final Location loc = window.location;
-    final hash = loc.hash;
-    final href = loc.href;
-
-    final History history = window.history;
-    switch(hash) {
-      case "#reset":
-        assert(href.endsWith(hash));
-        var newLoc = href.substring(0, href.length - hash.length);
-
-        window.localStorage.clear();
-
-        loc.replace(newLoc);
-        break;
-      case _BIG_HASH:
-        loc.reload();
-        break;
-      case _ABOUT_HASH:
-        _aboutController.add(null);
-        break;
-    }
-  }
-}