Make Flex,Row,Column const for real (#119673)

* Make Flex,Row,Column const for real

* dart fix --apply

* fix snippets

* fix integration test

* add comment

Author: goderbauer

dev/automated_tests/flutter_test/print_correct_local_widget_test.dart

@@ -14,15 +14,15 @@ void main() {
           appBar: AppBar(
             title: const Text('RenderFlex OverFlow'),
           ),
-          body: SizedBox(
+          body: const SizedBox(
             width: 400.0,
             child: Row(
               children: <Widget>[
-                const Icon(Icons.message),
+                Icon(Icons.message),
                 Column(
                   mainAxisSize: MainAxisSize.min,
                   crossAxisAlignment: CrossAxisAlignment.start,
-                  children: const <Widget>[
+                  children: <Widget>[
                     Text('Title'),
                     Text(
                       'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed '

dev/benchmarks/complex_layout/lib/src/app.dart

@@ -279,11 +279,11 @@ class IconBar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Padding(
-      padding: const EdgeInsets.only(left: 16.0, right: 16.0),
+    return const Padding(
+      padding: EdgeInsets.only(left: 16.0, right: 16.0),
       child: Row(
         mainAxisAlignment: MainAxisAlignment.spaceBetween,
-        children: const <Widget>[
+        children: <Widget>[
           IconWithText(Icons.thumb_up, 'Like'),
           IconWithText(Icons.comment, 'Comment'),
           IconWithText(Icons.share, 'Share'),
@@ -578,9 +578,9 @@ class BottomBar extends StatelessWidget {
           ),
         ),
       ),
-      child: Row(
+      child: const Row(
         mainAxisAlignment: MainAxisAlignment.spaceBetween,
-        children: const <Widget>[
+        children: <Widget>[
           BottomBarButton(Icons.new_releases, 'News'),
           BottomBarButton(Icons.people, 'Requests'),
           BottomBarButton(Icons.chat, 'Messenger'),

dev/benchmarks/macrobenchmarks/lib/src/cubic_bezier.dart

@@ -12,10 +12,10 @@ class CubicBezierPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Center(
+    return const Center(
       child: Column(
         mainAxisAlignment: MainAxisAlignment.center,
-        children: const <Widget>[
+        children: <Widget>[
           Bezier(Colors.amber, 1.0),
         ],
       ),

dev/benchmarks/macrobenchmarks/lib/src/stack_size.dart

@@ -88,9 +88,9 @@ class StackSizePage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Material(
+    return const Material(
       child: Column(
-        children: const <Widget>[
+        children: <Widget>[
           SizedBox(
             width: 200,
             height: 100,

dev/benchmarks/macrobenchmarks/lib/src/text.dart

@@ -9,10 +9,10 @@ class TextPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Material(
+    return const Material(
       child: Column(
         mainAxisAlignment: MainAxisAlignment.center,
-        children: const <Widget>[
+        children: <Widget>[
           SizedBox(
             width: 200,
             height: 100,

dev/benchmarks/macrobenchmarks/lib/src/web/bench_simple_lazy_text_scroll.dart

@@ -20,10 +20,10 @@ class BenchSimpleLazyTextScroll extends WidgetRecorder {
 
   @override
   Widget createWidget() {
-    return Directionality(
+    return const Directionality(
       textDirection: TextDirection.ltr,
       child: Row(
-        children: const <Widget>[
+        children: <Widget>[
           Flexible(
             child: _TestScrollingWidget(
               initialScrollOffset: 0,

dev/benchmarks/microbenchmarks/lib/foundation/all_elements_bench.dart

@@ -28,8 +28,8 @@ Future<void> main() async {
                   Icon(Icons.ac_unit),
                 ],
               ),
-              body: Column(
-                children: const <Widget>[
+              body: const Column(
+                children: <Widget>[
                   Text('Item 1'),
                   Text('Item 2'),
                   Text('Item 3'),

dev/benchmarks/test_apps/stocks/lib/stock_home.dart

@@ -345,8 +345,8 @@ class _CreateCompanySheet extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Column(
-      children: const <Widget>[
+    return const Column(
+      children: <Widget>[
         TextField(
           autofocus: true,
           decoration: InputDecoration(

dev/integration_tests/abstract_method_smoke_test/lib/main.dart

@@ -59,9 +59,9 @@ class SecondPage extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Scaffold(
+    return const Scaffold(
       body: Column(
-        children: const <Widget>[
+        children: <Widget>[
           Expanded(
             child: AndroidView(viewType: 'simple')
           ),

dev/integration_tests/flutter_gallery/lib/demo/cupertino/cupertino_switch_demo.dart

@@ -57,8 +57,8 @@ class _CupertinoSwitchDemoState extends State<CupertinoSwitchDemo> {
                 ),
                 Semantics(
                   container: true,
-                  child: Column(
-                    children: const <Widget>[
+                  child: const Column(
+                    children: <Widget>[
                       CupertinoSwitch(
                         value: true,
                         onChanged: null,
@@ -71,8 +71,8 @@ class _CupertinoSwitchDemoState extends State<CupertinoSwitchDemo> {
                 ),
                 Semantics(
                   container: true,
-                  child: Column(
-                    children: const <Widget>[
+                  child: const Column(
+                    children: <Widget>[
                       CupertinoSwitch(
                         value: false,
                         onChanged: null,