add structure

lib/widget/banner.dart

@@ -0,0 +1,35 @@
+import 'package:flutter/material.dart';
+
+import '../config.dart';
+
+class FlavorBanner extends StatelessWidget {
+  final Widget child;
+  FlavorBanner({@required this.child});
+  
+  @override
+  Widget build(BuildContext context) {
+    if(Config.isProduction()) return child;
+    return Stack(
+      children: <Widget>[
+        child,
+        _buildBanner(context)
+      ],
+    );
+  }
+  
+  Widget _buildBanner(BuildContext context) {
+    return Container(
+      width: 50,
+      height: 50,
+      child: CustomPaint(
+        painter: BannerPainter(
+          message: Config.instance.name,
+          textDirection: Directionality.of(context),
+          layoutDirection: Directionality.of(context),
+          location: BannerLocation.topStart,
+          color: Config.instance.color
+        ),
+      ),
+    );
+  }
+}