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.g.dart

@@ -0,0 +1,83 @@
+/*
+ * 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.
+ */
+
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'locations.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+LatLng _$LatLngFromJson(Map<String, dynamic> json) => LatLng(
+      lat: (json['lat'] as num).toDouble(),
+      lng: (json['lng'] as num).toDouble(),
+    );
+
+Map<String, dynamic> _$LatLngToJson(LatLng instance) => <String, dynamic>{
+      'lat': instance.lat,
+      'lng': instance.lng,
+    };
+
+Region _$RegionFromJson(Map<String, dynamic> json) => Region(
+      coords: LatLng.fromJson(json['coords'] as Map<String, dynamic>),
+      id: json['id'] as String,
+      name: json['name'] as String,
+      zoom: (json['zoom'] as num).toDouble(),
+    );
+
+Map<String, dynamic> _$RegionToJson(Region instance) => <String, dynamic>{
+      'coords': instance.coords,
+      'id': instance.id,
+      'name': instance.name,
+      'zoom': instance.zoom,
+    };
+
+Office _$OfficeFromJson(Map<String, dynamic> json) => Office(
+      address: json['address'] as String,
+      id: json['id'] as String,
+      image: json['image'] as String,
+      lat: (json['lat'] as num).toDouble(),
+      lng: (json['lng'] as num).toDouble(),
+      name: json['name'] as String,
+      phone: json['phone'] as String,
+      region: json['region'] as String,
+    );
+
+Map<String, dynamic> _$OfficeToJson(Office instance) => <String, dynamic>{
+      'address': instance.address,
+      'id': instance.id,
+      'image': instance.image,
+      'lat': instance.lat,
+      'lng': instance.lng,
+      'name': instance.name,
+      'phone': instance.phone,
+      'region': instance.region,
+    };
+
+Locations _$LocationsFromJson(Map<String, dynamic> json) => Locations(
+      offices: (json['offices'] as List<dynamic>)
+          .map((e) => Office.fromJson(e as Map<String, dynamic>))
+          .toList(),
+      regions: (json['regions'] as List<dynamic>)
+          .map((e) => Region.fromJson(e as Map<String, dynamic>))
+          .toList(),
+    );
+
+Map<String, dynamic> _$LocationsToJson(Locations instance) => <String, dynamic>{
+      'offices': instance.offices,
+      'regions': instance.regions,
+    };