[federated_plugin] adds web implementation of federated_plugin (#507)

experimental/federated_plugin/federated_plugin_web/lib/federated_plugin_web.dart

@@ -0,0 +1,45 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:html' as html;
+
+import 'package:federated_plugin_platform_interface/federated_plugin_platform_interface.dart';
+import 'package:federated_plugin_platform_interface/location_model.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_web_plugins/flutter_web_plugins.dart';
+
+/// Web Implementation of [FederatedPluginInterface] to provide location.
+class FederatedPlugin extends FederatedPluginInterface {
+  final html.Geolocation _geolocation;
+
+  /// Constructor to override the geolocation object for testing purpose.
+  FederatedPlugin({html.Geolocation geolocation})
+      : _geolocation = geolocation ?? html.window.navigator.geolocation;
+
+  /// Method to register the plugin which sets [FederatedPlugin] to be the default
+  /// instance of [FederatedPluginInterface].
+  static void registerWith(Registrar registrar) {
+    FederatedPluginInterface.instance = FederatedPlugin();
+  }
+
+  /// Returns [Location] to provide latitude and longitude.
+  ///
+  /// If any error, it's assume that user has denied the permission forever.
+  @override
+  Future<Location> getLocation() async {
+    try {
+      final geoPosition = await _geolocation.getCurrentPosition();
+      return Location(
+        longitude: geoPosition.coords.longitude.toDouble(),
+        latitude: geoPosition.coords.latitude.toDouble(),
+      );
+    } catch (error) {
+      throw PlatformException(
+        code: 'PERMISSION_DENIED',
+        message: 'Permission denied from User',
+        details: null,
+      );
+    }
+  }
+}