Add flutter_web samples (#75)

web/gallery/lib/gallery/about.dart

@@ -0,0 +1,78 @@
+// 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/gestures.dart';
+import 'package:flutter_web/material.dart';
+
+class _LinkTextSpan extends TextSpan {
+  // Beware!
+  //
+  // This class is only safe because the TapGestureRecognizer is not
+  // given a deadline and therefore never allocates any resources.
+  //
+  // In any other situation -- setting a deadline, using any of the less trivial
+  // recognizers, etc -- you would have to manage the gesture recognizer's
+  // lifetime and call dispose() when the TextSpan was no longer being rendered.
+  //
+  // Since TextSpan itself is @immutable, this means that you would have to
+  // manage the recognizer from outside the TextSpan, e.g. in the State of a
+  // stateful widget that then hands the recognizer to the TextSpan.
+
+  _LinkTextSpan({TextStyle style, String url, String text})
+      : super(
+            style: style,
+            text: text ?? url,
+            recognizer: TapGestureRecognizer()
+              ..onTap = () {
+                //launch(url, forceSafariVC: false);
+              });
+}
+
+void showGalleryAboutDialog(BuildContext context) {
+  final ThemeData themeData = Theme.of(context);
+  final TextStyle aboutTextStyle = themeData.textTheme.body2;
+  final TextStyle linkStyle =
+      themeData.textTheme.body2.copyWith(color: themeData.accentColor);
+
+  showAboutDialog(
+    context: context,
+    applicationVersion: '2018 Preview',
+    //applicationIcon: const FlutterLogo(),
+    applicationLegalese: '© 2018 The Chromium Authors',
+    children: <Widget>[
+      Padding(
+        padding: const EdgeInsets.only(top: 24.0),
+        child: RichText(
+          text: TextSpan(
+            children: <TextSpan>[
+              TextSpan(
+                  style: aboutTextStyle,
+                  text: 'Flutter web is an early-stage, web framework. '
+                      'This gallery is a preview of '
+                      "Flutter's many widgets, behaviors, animations, layouts, "
+                      'and more. Learn more about Flutter at '),
+              _LinkTextSpan(
+                style: linkStyle,
+                url: 'https://flutter.io',
+              ),
+              TextSpan(
+                style: aboutTextStyle,
+                text: '.\n\nTo see the source code for flutter ',
+              ),
+              _LinkTextSpan(
+                style: linkStyle,
+                url: 'https://goo.gl/iv1p4G',
+                text: 'flutter github repo',
+              ),
+              TextSpan(
+                style: aboutTextStyle,
+                text: '.',
+              ),
+            ],
+          ),
+        ),
+      ),
+    ],
+  );
+}