Remove fancy lines demo from Gallery (#4323)

This demo burns battery continuously even when there's no change to the visual
appearance. This patch removes this demo to avoid giving the impression that
Flutter burns battery.

Related to #4120

examples/flutter_gallery/lib/demo/all.dart

@@ -10,7 +10,6 @@ export 'colors_demo.dart';
 export 'data_table_demo.dart';
 export 'date_picker_demo.dart';
 export 'dialog_demo.dart';
-export 'drawing_demo.dart';
 export 'drop_down_demo.dart';
 export 'fitness_demo.dart';
 export 'flexible_space_demo.dart';

examples/flutter_gallery/lib/demo/drawing_demo.dart

-// 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 'dart:async';
-
-import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
-
-import 'package:flutter_sprites/flutter_sprites.dart';
-
-class DrawingDemo extends StatefulWidget {
-  static const String routeName = '/drawing';
-
-  @override
-  _DrawingDemoState createState() => new _DrawingDemoState();
-}
-
-class _DrawingDemoState extends State<DrawingDemo> {
-  _LineDrawingNode _rootNode;
-  ImageMap _images;
-
-  Future<Null> _loadAssets(AssetBundle bundle) async {
-    _images = new ImageMap(bundle);
-    await _images.load(<String>[
-      'packages/flutter_gallery_assets/fancylines.png'
-    ]);
-  }
-
-  @override
-  void initState() {
-    super.initState();
-    _loadAssets(DefaultAssetBundle.of(context)).then((_) {
-      setState(() {
-        _rootNode = new _LineDrawingNode(_images);
-      });
-    });
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    Widget body;
-    if (_rootNode == null) {
-      body = new Center(
-        child: new CircularProgressIndicator()
-      );
-    } else {
-      body = new SpriteWidget(_rootNode, SpriteBoxTransformMode.nativePoints);
-    }
-
-    return new Scaffold(
-      appBar: new AppBar(
-        title: new Text('Fancy lines')
-      ),
-      body: body
-    );
-  }
-}
-
-class _LineDrawingNode extends NodeWithSize {
-  _LineDrawingNode(this._images) : super(const Size(1024.0, 1024.0)) {
-    userInteractionEnabled = true;
-  }
-
-  final ImageMap _images;
-  EffectLine _currentLine;
-
-  @override
-  bool handleEvent(SpriteBoxEvent event) {
-    if (event.type == PointerDownEvent) {
-      _currentLine = new EffectLine(
-        texture: new Texture(_images['packages/flutter_gallery_assets/fancylines.png']),
-        colorSequence: new ColorSequence.fromStartAndEndColor(Colors.purple[500], Colors.purple[600]),
-        fadeAfterDelay: 3.0,
-        fadeDuration: 1.0
-      );
-      _currentLine.addPoint(event.boxPosition);
-      addChild(_currentLine);
-    } else if (event.type == PointerMoveEvent) {
-      _currentLine.addPoint(event.boxPosition);
-    }
-
-    return true;
-  }
-}

examples/flutter_gallery/lib/gallery/app.dart

@@ -11,7 +11,6 @@ import 'home.dart';
 final Map<String, WidgetBuilder> kRoutes = <String, WidgetBuilder>{
   WeatherDemo.routeName: (BuildContext context) => new WeatherDemo(),
   FitnessDemo.routeName: (BuildContext context) => new FitnessDemo(),
-  DrawingDemo.routeName: (BuildContext context) => new DrawingDemo(),
   Calculator.routeName: (BuildContext context) => new Calculator(),
   FlexibleSpaceDemo.routeName: (BuildContext context) => new FlexibleSpaceDemo(),
   TabsFabDemo.routeName: (BuildContext context) => new TabsFabDemo(),

examples/flutter_gallery/lib/gallery/home.dart

@@ -75,7 +75,6 @@ class GalleryHomeState extends State<GalleryHome> {
             children: <Widget>[
               new GalleryItem(title: 'Weather', routeName: WeatherDemo.routeName),
               new GalleryItem(title: 'Fitness', routeName: FitnessDemo.routeName),
-              new GalleryItem(title: 'Fancy lines', routeName: DrawingDemo.routeName),
               new GalleryItem(title: 'Calculator', routeName: Calculator.routeName),
               new GalleryItem(title: 'Flexible space toolbar', routeName: FlexibleSpaceDemo.routeName),
               new GalleryItem(title: 'Floating action button', routeName: TabsFabDemo.routeName),