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/slide_puzzle/lib/src/widgets/decoration_image_plus.dart

@@ -1,12 +1,8 @@
-// Copyright 2019 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.
-
 // ignore_for_file: omit_local_variable_types, annotate_overrides
 
-import 'package:flutter_web_ui/ui.dart' as ui show Image;
+import 'dart:ui' as ui show Image;
 
-import '../flutter.dart';
+import 'package:flutter/material.dart';
 
 // A model on top of DecorationImage that supports slicing up the source image
 // efficiently to draw it as tiles in the puzzle game
@@ -142,13 +138,13 @@ class DecorationImagePlus implements DecorationImage {
 
   @override
   String toString() {
-    final List<String> properties = <String>['$image'];
+    final List<String> properties = <String>[];
+    properties.add('$image');
     if (colorFilter != null) properties.add('$colorFilter');
     if (fit != null &&
         !(fit == BoxFit.fill && centerSlice != null) &&
-        !(fit == BoxFit.scaleDown && centerSlice == null)) {
+        !(fit == BoxFit.scaleDown && centerSlice == null))
       properties.add('$fit');
-    }
     properties.add('$alignment');
     if (centerSlice != null) properties.add('centerSlice: $centerSlice');
     if (repeat != ImageRepeat.noRepeat) properties.add('$repeat');
@@ -170,13 +166,16 @@ class DecorationImagePlus implements DecorationImage {
 /// longer needed.
 class DecorationImagePainterPlus implements DecorationImagePainter {
   DecorationImagePainterPlus._(this._details, this._onChanged)
-      : assert(_details != null);
+      : assert(_details != null) {
+    _imageStreamListener = ImageStreamListener(_imageListener);
+  }
 
   final DecorationImagePlus _details;
   final VoidCallback _onChanged;
 
   ImageStream _imageStream;
   ImageInfo _image;
+  ImageStreamListener _imageStreamListener;
 
   /// Draw the image onto the given canvas.
   ///
@@ -218,15 +217,14 @@ class DecorationImagePainterPlus implements DecorationImagePainter {
 
     final ImageStream newImageStream = _details.image.resolve(configuration);
     if (newImageStream.key != _imageStream?.key) {
-      _imageStream?.removeListener(_imageListener);
-      _imageStream = newImageStream..addListener(_imageListener);
+      _imageStream?.removeListener(_imageStreamListener);
+      _imageStream = newImageStream..addListener(_imageStreamListener);
     }
     if (_image == null) return;
 
     if (clipPath != null) {
-      canvas
-        ..save()
-        ..clipPath(clipPath);
+      canvas.save();
+      canvas.clipPath(clipPath);
     }
 
     _paintImage(
@@ -259,7 +257,7 @@ class DecorationImagePainterPlus implements DecorationImagePainter {
   /// After this method has been called, the object is no longer usable.
   @mustCallSuper
   void dispose() {
-    _imageStream?.removeListener(_imageListener);
+    _imageStream?.removeListener(_imageStreamListener);
   }
 
   @override

web/slide_puzzle/lib/src/widgets/material_interior_alt.dart

@@ -1,8 +1,4 @@
-// Copyright 2019 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 '../flutter.dart';
+import 'package:flutter/material.dart';
 
 // Copied from
 // https://github.com/flutter/flutter/blob/f5b02e3c05ed1ab31e890add84fb56e35de2d392/packages/flutter/lib/src/material/material.dart#L593-L715