add platform interface stub

@@ -12,6 +12,7 @@ export 'src/enums/torch_state.dart';
 export 'src/mobile_scanner.dart';
 export 'src/mobile_scanner_controller.dart';
 export 'src/mobile_scanner_exception.dart';
+export 'src/mobile_scanner_platform_interface.dart';
 export 'src/objects/address.dart';
 export 'src/objects/barcode.dart';
 export 'src/objects/barcode_capture.dart';

+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+import 'package:mobile_scanner/src/mobile_scanner_platform_interface.dart';
+
+/// An implementation of [MobileScannerPlatform] that uses method channels.
+class MethodChannelMobileScanner extends MobileScannerPlatform {
+  /// The method channel used to interact with the native platform.
+  @visibleForTesting
+  final methodChannel = const MethodChannel('dev.steenbakker.mobile_scanner/scanner/method');
+
+  /// The event channel that sends back scanned barcode events.
+  @visibleForTesting
+  final eventChannel = const EventChannel('dev.steenbakker.mobile_scanner/scanner/event');
+}

+import 'package:mobile_scanner/src/method_channel/mobile_scanner_method_channel.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+/// The platform interface for the `mobile_scanner` plugin.
+abstract class MobileScannerPlatform extends PlatformInterface {
+  /// Constructs a MobileScannerPlatform.
+  MobileScannerPlatform() : super(token: _token);
+
+  static final Object _token = Object();
+
+  static MobileScannerPlatform _instance = MethodChannelMobileScanner();
+
+  /// The default instance of [MobileScannerPlatform] to use.
+  ///
+  /// Defaults to [MethodChannelMobileScanner].
+  static MobileScannerPlatform get instance => _instance;
+
+  /// Platform-specific implementations should set this with their own
+  /// platform-specific class that extends [MobileScannerPlatform] when
+  /// they register themselves.
+  static set instance(MobileScannerPlatform instance) {
+    PlatformInterface.verifyToken(instance, _token);
+    _instance = instance;
+  }
+}

@@ -25,6 +25,7 @@ dependencies:
   flutter_web_plugins:
     sdk: flutter
   js: ">=0.6.3 <0.8.0"
+  plugin_platform_interface: ^2.0.2    
 
 dev_dependencies:
   flutter_test: