Update web/ samples to work with Flutter SDK (#134)

* add package:http dependency in dad_jokes

* add package:http dependency in filipino_cuisine

* don't build package:http demos until flutter/flutter#34858 is resolved

* update gallery

* update github_dataviz

* update particle_background

* don't build github_dataviz (uses package:http)

* update slide_puzzle

* update spinning_square

* update timeflow

* update vision_challenge

* update charts

* update dad_jokes

* update filipino cuisine

* ignore build output

* update timeflow and vision_challenge

* update slide_puzzle

* don't commit build/ directory

* move preview.png images to assets

* fix path url join

* update readme

* update web/readme.md

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

@@ -1,24 +1,25 @@
-// Copyright 2018 The Chromium Authors. All rights reserved.
+// Copyright 2016 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/material.dart';
+
 import '../../gallery/demo.dart';
 
 const String _text1 =
-    'Snackbars provide lightweight feedback about an operation by '
-    'showing a brief message at the bottom of the screen. Snackbars '
-    'can contain an action.';
+  'Snackbars provide lightweight feedback about an operation by '
+  'showing a brief message at the bottom of the screen. Snackbars '
+  'can contain an action.';
 
 const String _text2 =
-    'Snackbars should contain a single line of text directly related '
-    'to the operation performed. They cannot contain icons.';
+  'Snackbars should contain a single line of text directly related '
+  'to the operation performed. They cannot contain icons.';
 
 const String _text3 =
-    'By default snackbars automatically disappear after a few seconds ';
+  'By default snackbars automatically disappear after a few seconds ';
 
 class SnackBarDemo extends StatefulWidget {
-  const SnackBarDemo({Key key}) : super(key: key);
+  const SnackBarDemo({ Key key }) : super(key: key);
 
   static const String routeName = '/material/snack-bar';
 
@@ -34,50 +35,61 @@ class _SnackBarDemoState extends State<SnackBarDemo> {
       top: false,
       bottom: false,
       child: ListView(
-          padding: const EdgeInsets.all(24.0),
-          children: <Widget>[
-            const Text(_text1),
-            const Text(_text2),
-            Center(
-              child: Row(children: <Widget>[
-                RaisedButton(
-                    child: const Text('SHOW A SNACKBAR'),
+        padding: const EdgeInsets.all(24.0),
+        children: <Widget>[
+          const Text(_text1),
+          const Text(_text2),
+          Center(
+            child: RaisedButton(
+              child: const Text('SHOW A SNACKBAR'),
+              onPressed: () {
+                final int thisSnackBarIndex = _snackBarIndex++;
+                Scaffold.of(context).showSnackBar(SnackBar(
+                  content: Text('This is snackbar #$thisSnackBarIndex.'),
+                  action: SnackBarAction(
+                    label: 'ACTION',
                     onPressed: () {
-                      final int thisSnackBarIndex = _snackBarIndex++;
                       Scaffold.of(context).showSnackBar(SnackBar(
-                        content: Text('This is snackbar #$thisSnackBarIndex.'),
-                        action: SnackBarAction(
-                            label: 'ACTION',
-                            onPressed: () {
-                              Scaffold.of(context).showSnackBar(SnackBar(
-                                  content: Text(
-                                      'You pressed snackbar $thisSnackBarIndex\'s action.')));
-                            }),
+                        content: Text('You pressed snackbar $thisSnackBarIndex\'s action.'),
                       ));
-                    }),
-              ]),
+                    },
+                  ),
+                ));
+              },
             ),
-            const Text(_text3),
-          ].map<Widget>((Widget child) {
-            return Container(
-                margin: const EdgeInsets.symmetric(vertical: 12.0),
-                child: child);
-          }).toList()),
+          ),
+          const Text(_text3),
+        ]
+        .map<Widget>((Widget child) {
+          return Container(
+            margin: const EdgeInsets.symmetric(vertical: 12.0),
+            child: child,
+          );
+        })
+        .toList(),
+      ),
     );
   }
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-        appBar: AppBar(
-          title: const Text('Snackbar'),
-          actions: <Widget>[
-            MaterialDemoDocumentationButton(SnackBarDemo.routeName)
-          ],
-        ),
-        body: Builder(
-            // Create an inner BuildContext so that the snackBar onPressed methods
-            // can refer to the Scaffold with Scaffold.of().
-            builder: buildBody));
+      appBar: AppBar(
+        title: const Text('Snackbar'),
+        actions: <Widget>[MaterialDemoDocumentationButton(SnackBarDemo.routeName)],
+      ),
+      body: Builder(
+        // Create an inner BuildContext so that the snackBar onPressed methods
+        // can refer to the Scaffold with Scaffold.of().
+        builder: buildBody
+      ),
+      floatingActionButton: FloatingActionButton(
+        child: const Icon(Icons.add),
+        tooltip: 'Create',
+        onPressed: () {
+          print('Floating Action Button was pressed');
+        }
+      ),
+    );
   }
 }