Add flutter_web samples (#75)

web/gallery/lib/gallery/demo.dart

@@ -0,0 +1,201 @@
+// Copyright 2018 The Chromium Authors. 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_web/material.dart';
+import 'package:flutter_web/cupertino.dart';
+
+class ComponentDemoTabData {
+  ComponentDemoTabData({
+    this.demoWidget,
+    this.exampleCodeTag,
+    this.description,
+    this.tabName,
+    this.documentationUrl,
+  });
+
+  final Widget demoWidget;
+  final String exampleCodeTag;
+  final String description;
+  final String tabName;
+  final String documentationUrl;
+
+  @override
+  bool operator ==(Object other) {
+    if (other.runtimeType != runtimeType) return false;
+    final ComponentDemoTabData typedOther = other;
+    return typedOther.tabName == tabName &&
+        typedOther.description == description &&
+        typedOther.documentationUrl == documentationUrl;
+  }
+
+  @override
+  int get hashCode => hashValues(tabName, description, documentationUrl);
+}
+
+class TabbedComponentDemoScaffold extends StatelessWidget {
+  const TabbedComponentDemoScaffold({
+    this.title,
+    this.demos,
+    this.actions,
+  });
+
+  final List<ComponentDemoTabData> demos;
+  final String title;
+  final List<Widget> actions;
+
+  void _showExampleCode(BuildContext context) {
+    final String tag =
+        demos[DefaultTabController.of(context).index].exampleCodeTag;
+    if (tag != null) {
+      throw new UnimplementedError();
+      // TODO:
+//      Navigator.push(context, MaterialPageRoute<FullScreenCodeDialog>(
+//          builder: (BuildContext context) => FullScreenCodeDialog(exampleCodeTag: tag)
+//      ));
+    }
+  }
+
+  void _showApiDocumentation(BuildContext context) {
+    final String url =
+        demos[DefaultTabController.of(context).index].documentationUrl;
+    if (url != null) {
+      // launch(url, forceWebView: true);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return DefaultTabController(
+      length: demos.length,
+      child: Scaffold(
+        appBar: AppBar(
+          title: Text(title),
+          actions: (actions ?? <Widget>[])
+            ..addAll(
+              <Widget>[
+                Builder(
+                  builder: (BuildContext context) {
+                    return IconButton(
+                      icon: const Icon(Icons.library_books),
+                      onPressed: () => _showApiDocumentation(context),
+                    );
+                  },
+                ),
+                Builder(
+                  builder: (BuildContext context) {
+                    return IconButton(
+                      icon: const Icon(Icons.code),
+                      tooltip: 'Show example code',
+                      onPressed: () => _showExampleCode(context),
+                    );
+                  },
+                )
+              ],
+            ),
+          bottom: TabBar(
+            isScrollable: true,
+            tabs: demos
+                .map<Widget>(
+                    (ComponentDemoTabData data) => Tab(text: data.tabName))
+                .toList(),
+          ),
+        ),
+        body: TabBarView(
+          children: demos.map<Widget>((ComponentDemoTabData demo) {
+            return SafeArea(
+              top: false,
+              bottom: false,
+              child: Column(
+                children: <Widget>[
+                  Padding(
+                      padding: const EdgeInsets.all(16.0),
+                      child: Text(demo.description,
+                          style: Theme.of(context).textTheme.subhead)),
+                  Expanded(child: demo.demoWidget)
+                ],
+              ),
+            );
+          }).toList(),
+        ),
+      ),
+    );
+  }
+}
+
+class MaterialDemoDocumentationButton extends StatelessWidget {
+  MaterialDemoDocumentationButton(String routeName, {Key key})
+      : documentationUrl = 'todo',
+        assert(
+          'todo' != null,
+          'A documentation URL was not specified for demo route $routeName in kAllGalleryDemos',
+        ),
+        super(key: key);
+
+  final String documentationUrl;
+
+  @override
+  Widget build(BuildContext context) {
+    return IconButton(
+        icon: const Icon(Icons.library_books),
+        tooltip: 'API documentation',
+        // TODO(flutter_web): launch(documentationUrl, forceWebView: true)
+        onPressed: () => {});
+  }
+}
+
+Widget wrapScaffold(String title, BuildContext context, Key key, Widget child,
+    String routeName) {
+  IconData _backIcon() {
+    switch (Theme.of(context).platform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+        return Icons.arrow_back;
+      case TargetPlatform.iOS:
+        return Icons.arrow_back_ios;
+    }
+    assert(false);
+    return null;
+  }
+
+  return Scaffold(
+    key: key,
+    appBar: AppBar(
+      leading: IconButton(
+        icon: Icon(_backIcon()),
+        alignment: Alignment.centerLeft,
+        tooltip: 'Back',
+        onPressed: () {
+          Navigator.pop(context);
+        },
+      ),
+      title: Text(title),
+      actions: <Widget>[MaterialDemoDocumentationButton(routeName)],
+    ),
+    body: Material(child: Center(child: child)),
+  );
+}
+
+class CupertinoDemoDocumentationButton extends StatelessWidget {
+  CupertinoDemoDocumentationButton(String routeName, {Key key})
+      : documentationUrl = 'todo',
+        assert(
+          'todo' != null,
+          'A documentation URL was not specified for demo route $routeName in kAllGalleryDemos',
+        ),
+        super(key: key);
+
+  final String documentationUrl;
+
+  @override
+  Widget build(BuildContext context) {
+    return CupertinoButton(
+        padding: EdgeInsets.zero,
+        child: Semantics(
+          label: 'API documentation',
+          child: const Icon(CupertinoIcons.book),
+        ),
+        // TODO(flutter_web): launch(documentationUrl, forceWebView: true)
+        onPressed: () => {});
+  }
+}