Rework of "Lay out a widget" + use of code-excerpts

Contributes to #2233

Author: chalin

examples/layout/base/README.md

@@ -1 +1 @@
-../../../README.md
+../../README.md

examples/layout/base/lib/main.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 
 void main() => runApp(MyApp());
 
+// #docregion MyApp
 class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
@@ -11,9 +12,13 @@ class MyApp extends StatelessWidget {
         appBar: AppBar(
           title: Text('Flutter layout demo'),
         ),
+        // #docregion centered-text
         body: Center(
+          // #docregion text
           child: Text('Hello World'),
+          // #enddocregion text
         ),
+        // #enddocregion centered-text
       ),
     );
   }

examples/layout/lakes/step5/lib/main.dart

@@ -34,10 +34,12 @@ class MyApp extends StatelessWidget {
             ),
           ),
           /*3*/
+          // #docregion Icon
           Icon(
             Icons.star,
             color: Colors.red[500],
           ),
+          // #enddocregion Icon
           Text('41'),
         ],
       ),
@@ -79,12 +81,14 @@ class MyApp extends StatelessWidget {
         ),
         body: Column(
           children: [
+            // #docregion Image-asset
             Image.asset(
               'images/lake.jpg',
               width: 600.0,
               height: 240.0,
               fit: BoxFit.cover,
             ),
+            // #enddocregion Image-asset
             titleSection,
             buttonSection,
             textSection,

examples/layout/non_material/README.md

@@ -0,0 +1 @@
+../../README.md

src/_includes/code/layout/widgets-only/main.dart renamed to examples/layout/non_material/lib/main.dart

@@ -1,26 +1,27 @@
-// Copyright 2017 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.
-
-// This app doesn't use any material widgets, such as Scaffold.
+// This app doesn't use any Material widgets, such as Scaffold.
 // Normally, an app that doesn't use Scaffold has a black background
 // and the default text color is black. This app changes its background
 // to white and its text color to dark grey to mimic a material app.
+
 import 'package:flutter/material.dart';
 
-void main() {
-  runApp(MyApp());
-}
+void main() => runApp(MyApp());
 
+// #docregion MyApp
 class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Container(
       decoration: BoxDecoration(color: Colors.white),
       child: Center(
-        child: Text('Hello World',
-            textDirection: TextDirection.ltr,
-            style: TextStyle(fontSize: 40.0, color: Colors.black87)),
+        child: Text(
+          'Hello World',
+          textDirection: TextDirection.ltr,
+          style: TextStyle(
+            fontSize: 32.0,
+            color: Colors.black87,
+          ),
+        ),
       ),
     );
   }

examples/layout/non_material/pubspec.yaml

@@ -0,0 +1,19 @@
+name: layout
+description: >
+  Sample app from "Building Layouts", https://flutter.io/docs/development/ui/layout.
+version: 1.0.0
+
+environment:
+  sdk: '>=2.0.0-dev.68.0 <3.0.0'
+
+dependencies:
+  flutter:
+    sdk: flutter
+  cupertino_icons: ^0.1.2
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+
+flutter:
+  uses-material-design: true

examples/layout/non_material/test/widget_test.dart

@@ -0,0 +1,12 @@
+// Basic Flutter widget test. Learn more at https://flutter.io/docs/testing.
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:layout/main.dart';
+
+void main() {
+  testWidgets('Codelab smoke test', (WidgetTester tester) async {
+    await tester.pumpWidget(new MyApp());
+    expect(find.text('Hello World'), findsOneWidget);
+  });
+}