Add flutter_web samples (#75)

web/gallery/lib/demo/material/progress_indicator_demo.dart

@@ -0,0 +1,132 @@
+// 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 '../../gallery/demo.dart';
+
+class ProgressIndicatorDemo extends StatefulWidget {
+  static const String routeName = '/material/progress-indicator';
+
+  @override
+  _ProgressIndicatorDemoState createState() => _ProgressIndicatorDemoState();
+}
+
+class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo>
+    with SingleTickerProviderStateMixin {
+  AnimationController _controller;
+  Animation<double> _animation;
+
+  @override
+  void initState() {
+    super.initState();
+    _controller = AnimationController(
+      duration: const Duration(milliseconds: 1500),
+      vsync: this,
+      animationBehavior: AnimationBehavior.preserve,
+    )..forward();
+
+    _animation = CurvedAnimation(
+        parent: _controller,
+        curve: const Interval(0.0, 0.9, curve: Curves.fastOutSlowIn),
+        reverseCurve: Curves.fastOutSlowIn)
+      ..addStatusListener((AnimationStatus status) {
+        if (status == AnimationStatus.dismissed)
+          _controller.forward();
+        else if (status == AnimationStatus.completed) _controller.reverse();
+      });
+  }
+
+  @override
+  void dispose() {
+    _controller.stop();
+    super.dispose();
+  }
+
+  void _handleTap() {
+    setState(() {
+      // valueAnimation.isAnimating is part of our build state
+      if (_controller.isAnimating) {
+        _controller.stop();
+      } else {
+        switch (_controller.status) {
+          case AnimationStatus.dismissed:
+          case AnimationStatus.forward:
+            _controller.forward();
+            break;
+          case AnimationStatus.reverse:
+          case AnimationStatus.completed:
+            _controller.reverse();
+            break;
+        }
+      }
+    });
+  }
+
+  Widget _buildIndicators(BuildContext context, Widget child) {
+    final List<Widget> indicators = <Widget>[
+      const SizedBox(width: 200.0, child: LinearProgressIndicator()),
+      const LinearProgressIndicator(),
+      const LinearProgressIndicator(),
+      LinearProgressIndicator(value: _animation.value),
+      Row(
+        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+        children: <Widget>[
+          const CircularProgressIndicator(),
+          SizedBox(
+              width: 20.0,
+              height: 20.0,
+              child: CircularProgressIndicator(value: _animation.value)),
+          SizedBox(
+            width: 100.0,
+            height: 20.0,
+            child: Text('${(_animation.value * 100.0).toStringAsFixed(1)}%',
+                textAlign: TextAlign.right),
+          ),
+        ],
+      ),
+    ];
+    return Column(
+      children: indicators
+          .map<Widget>((Widget c) => Container(
+              child: c,
+              margin:
+                  const EdgeInsets.symmetric(vertical: 15.0, horizontal: 20.0)))
+          .toList(),
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('Progress indicators'),
+        actions: <Widget>[
+          MaterialDemoDocumentationButton(ProgressIndicatorDemo.routeName)
+        ],
+      ),
+      body: Center(
+        child: SingleChildScrollView(
+          child: DefaultTextStyle(
+            style: Theme.of(context).textTheme.title,
+            child: GestureDetector(
+              onTap: _handleTap,
+              behavior: HitTestBehavior.opaque,
+              child: SafeArea(
+                top: false,
+                bottom: false,
+                child: Container(
+                  padding: const EdgeInsets.symmetric(
+                      vertical: 12.0, horizontal: 8.0),
+                  child: AnimatedBuilder(
+                      animation: _animation, builder: _buildIndicators),
+                ),
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}