Fix newly reported prefer_const_constructors lints. (#54176)

dev/automated_tests/flutter_test/print_correct_local_widget_test.dart

@@ -19,7 +19,7 @@ void main() {
             width: 400.0,
             child: Row(
               children: <Widget>[
-                Icon(Icons.message),
+                const Icon(Icons.message),
                 Column(
                   mainAxisSize: MainAxisSize.min,
                   crossAxisAlignment: CrossAxisAlignment.start,

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

@@ -32,7 +32,7 @@ class AnimatedPlaceholderPage extends StatelessWidget {
       gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 10),
       itemBuilder: (BuildContext context, int index) {
         return FadeInImage(
-          placeholder: DelayedBase64Image(Duration.zero, kAnimatedGif),
+          placeholder: const DelayedBase64Image(Duration.zero, kAnimatedGif),
           image: DelayedBase64Image(Duration(milliseconds: 100 * index), kBlueSquare),
         );
       },

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

@@ -66,7 +66,7 @@ class _BackdropFilterPageState extends State<BackdropFilterPage> with TickerProv
       backgroundColor: Colors.grey,
       body: Stack(
         children: <Widget>[
-          Text('0' * 10000, style: TextStyle(color: Colors.yellow)),
+          Text('0' * 10000, style: const TextStyle(color: Colors.yellow)),
           Column(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: <Widget>[

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

@@ -24,9 +24,9 @@ class _ColorFilterAndFadePageState extends State<ColorFilterAndFadePage> with Ti
       width: 24,
       height: 24,
       useColorFilter: _useColorFilter,
-      shadow: ui.Shadow(
+      shadow: const ui.Shadow(
         color: Colors.black45,
-        offset: const Offset(0.0, 2.0),
+        offset: Offset(0.0, 2.0),
         blurRadius: 4.0,
       ),
     );

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

@@ -263,7 +263,7 @@ class ListItem extends StatelessWidget {
           ),
           ConstrainedBox(
             constraints: const BoxConstraints(maxWidth: 250),
-            child: Text(
+            child: const Text(
               kMockName,
               maxLines: 1,
               overflow: TextOverflow.ellipsis,

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

@@ -52,7 +52,7 @@ class _PostBackdropFilterPageState extends State<PostBackdropFilterPage> with Ti
       backgroundColor: Colors.grey,
       body: Stack(
         children: <Widget>[
-          Text('0' * 10000, style: TextStyle(color: Colors.yellow)),
+          Text('0' * 10000, style: const TextStyle(color: Colors.yellow)),
           Column(
             mainAxisAlignment: MainAxisAlignment.spaceEvenly,
             children: <Widget>[

dev/integration_tests/android_splash_screens/splash_screen_kitchen_sink/lib/main.dart

@@ -108,7 +108,7 @@ class _MyHomePageState extends State<MyHomePage> {
       floatingActionButton: FloatingActionButton(
         onPressed: _incrementCounter,
         tooltip: 'Increment',
-        child: Icon(Icons.add),
+        child: const Icon(Icons.add),
       ), // This trailing comma makes auto-formatting nicer for build methods.
     );
   }

examples/image_list/lib/main.dart

@@ -210,7 +210,7 @@ class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
       floatingActionButton: FloatingActionButton(
         onPressed: _incrementCounter,
         tooltip: 'Increment',
-        child: Icon(Icons.add),
+        child: const Icon(Icons.add),
       ),
     );
   }

examples/splash/lib/main.dart

@@ -7,7 +7,7 @@ import 'package:flutter/material.dart';
 void main() {
   runApp(
     DecoratedBox(
-      decoration: BoxDecoration(color: Colors.white),
+      decoration: const BoxDecoration(color: Colors.white),
       child: Center(
         child: Column(
           mainAxisAlignment: MainAxisAlignment.center,

packages/flutter_localizations/test/text_test.dart

@@ -43,14 +43,14 @@ void main() {
                   },
                   itemBuilder: (BuildContext context) {
                     return <PopupMenuItem<int>>[
-                      PopupMenuItem<int>(
+                      const PopupMenuItem<int>(
                         value: 1,
                         child: Text(
                           'hello, world',
                           style: TextStyle(color: Colors.blue),
                         ),
                       ),
-                      PopupMenuItem<int>(
+                      const PopupMenuItem<int>(
                         value: 2,
                         child: Text(
                           '你好，世界',
@@ -129,14 +129,14 @@ void main() {
                   },
                   itemBuilder: (BuildContext context) {
                     return <PopupMenuItem<int>>[
-                      PopupMenuItem<int>(
+                      const PopupMenuItem<int>(
                         value: 1,
                         child: Text(
                           'hello, world',
                           style: TextStyle(color: Colors.blue),
                         ),
                       ),
-                      PopupMenuItem<int>(
+                      const PopupMenuItem<int>(
                         value: 2,
                         child: Text(
                           '你好，世界',

packages/flutter_tools/lib/src/ios/ios_emulators.dart

@@ -72,5 +72,5 @@ List<IOSEmulator> getEmulators() {
     return <IOSEmulator>[];
   }
 
-  return <IOSEmulator>[IOSEmulator(iosSimulatorId)];
+  return <IOSEmulator>[const IOSEmulator(iosSimulatorId)];
 }