[Gallery] Fix directory structure (#312)

gallery/lib/demos/material/tooltip_demo.dart

@@ -0,0 +1,46 @@
+// 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 tooltipDemo
+
+class TooltipDemo extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        automaticallyImplyLeading: false,
+        title: Text(GalleryLocalizations.of(context).demoTooltipTitle),
+      ),
+      body: Center(
+        child: Padding(
+          padding: const EdgeInsets.all(8),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              Text(
+                GalleryLocalizations.of(context).demoTooltipInstructions,
+                textAlign: TextAlign.center,
+              ),
+              SizedBox(height: 16),
+              Tooltip(
+                message:
+                    GalleryLocalizations.of(context).starterAppTooltipSearch,
+                child: IconButton(
+                  color: Theme.of(context).colorScheme.primary,
+                  onPressed: () {},
+                  icon: Icon(Icons.search),
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+// END