[Gallery] Fix directory structure (#312)

gallery/lib/demos/material/snackbar_demo.dart

@@ -0,0 +1,54 @@
+// Copyright 2019 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 'package:flutter/material.dart';
+import 'package:gallery/l10n/gallery_localizations.dart';
+
+// BEGIN snackbarsDemo
+
+class SnackbarsDemo extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        automaticallyImplyLeading: false,
+        title: Text(GalleryLocalizations.of(context).demoSnackbarsTitle),
+      ),
+      body: Builder(
+        // Create an inner BuildContext so that the snackBar onPressed methods
+        // can refer to the Scaffold with Scaffold.of().
+        builder: (context) {
+          return Center(
+            child: RaisedButton(
+              child: Text(
+                  GalleryLocalizations.of(context).demoSnackbarsButtonLabel),
+              onPressed: () {
+                Scaffold.of(context).hideCurrentSnackBar();
+                Scaffold.of(context).showSnackBar(SnackBar(
+                  content: Text(
+                    GalleryLocalizations.of(context).demoSnackbarsText,
+                  ),
+                  action: SnackBarAction(
+                    label: GalleryLocalizations.of(context)
+                        .demoSnackbarsActionButtonLabel,
+                    onPressed: () {
+                      Scaffold.of(context).hideCurrentSnackBar();
+                      Scaffold.of(context).showSnackBar(SnackBar(
+                        content: Text(
+                          GalleryLocalizations.of(context).demoSnackbarsAction,
+                        ),
+                      ));
+                    },
+                  ),
+                ));
+              },
+            ),
+          );
+        },
+      ),
+    );
+  }
+}
+
+// END