Added Google Maps sample code (#1671)

* Added Google Maps sample code

* Updated per @domesticmouse review

* Updated dependabot and pubspec for Dart 2.19

google_maps/lib/src/locations.dart

@@ -0,0 +1,121 @@
+/*
+ * Copyright 2019 Google LLC
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import 'dart:convert';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart' show rootBundle;
+import 'package:http/http.dart' as http;
+import 'package:json_annotation/json_annotation.dart';
+
+part 'locations.g.dart';
+
+@JsonSerializable()
+class LatLng {
+  LatLng({
+    required this.lat,
+    required this.lng,
+  });
+
+  factory LatLng.fromJson(Map<String, dynamic> json) => _$LatLngFromJson(json);
+  Map<String, dynamic> toJson() => _$LatLngToJson(this);
+
+  final double lat;
+  final double lng;
+}
+
+@JsonSerializable()
+class Region {
+  Region({
+    required this.coords,
+    required this.id,
+    required this.name,
+    required this.zoom,
+  });
+
+  factory Region.fromJson(Map<String, dynamic> json) => _$RegionFromJson(json);
+  Map<String, dynamic> toJson() => _$RegionToJson(this);
+
+  final LatLng coords;
+  final String id;
+  final String name;
+  final double zoom;
+}
+
+@JsonSerializable()
+class Office {
+  Office({
+    required this.address,
+    required this.id,
+    required this.image,
+    required this.lat,
+    required this.lng,
+    required this.name,
+    required this.phone,
+    required this.region,
+  });
+
+  factory Office.fromJson(Map<String, dynamic> json) => _$OfficeFromJson(json);
+  Map<String, dynamic> toJson() => _$OfficeToJson(this);
+
+  final String address;
+  final String id;
+  final String image;
+  final double lat;
+  final double lng;
+  final String name;
+  final String phone;
+  final String region;
+}
+
+@JsonSerializable()
+class Locations {
+  Locations({
+    required this.offices,
+    required this.regions,
+  });
+
+  factory Locations.fromJson(Map<String, dynamic> json) =>
+      _$LocationsFromJson(json);
+  Map<String, dynamic> toJson() => _$LocationsToJson(this);
+
+  final List<Office> offices;
+  final List<Region> regions;
+}
+
+Future<Locations> getGoogleOffices() async {
+  const googleLocationsURL = 'https://about.google/static/data/locations.json';
+
+  // Retrieve the locations of Google offices
+  try {
+    final response = await http.get(Uri.parse(googleLocationsURL));
+    if (response.statusCode == 200) {
+      return Locations.fromJson(
+          json.decode(response.body) as Map<String, dynamic>);
+    }
+  } catch (e) {
+    if (kDebugMode) {
+      print(e);
+    }
+  }
+
+  // Fallback for when the above HTTP request fails.
+  return Locations.fromJson(
+    json.decode(
+      await rootBundle.loadString('assets/locations.json'),
+    ) as Map<String, dynamic>,
+  );
+}