Fix new prefer_const_constructors after analyzer fix. (#39917)

dev/integration_tests/image_loading/lib/main.dart

@@ -42,7 +42,7 @@ class _ImageLoaderState extends State<ImageLoader> {
   void initState() {
     // This is not an image, but we don't care since we're using a faked
     // http client.
-    final NetworkImage image = NetworkImage('https://github.com/flutter/flutter');
+    const NetworkImage image = NetworkImage('https://github.com/flutter/flutter');
     final ImageStream stream = image.resolve(ImageConfiguration.empty);
     ImageStreamListener listener;
     listener = ImageStreamListener(

dev/integration_tests/web/lib/main.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/widgets.dart';
 
 void main() {
-  runApp(Center(
-    child: const Text('Hello, World', textDirection: TextDirection.ltr),
+  runApp(const Center(
+    child: Text('Hello, World', textDirection: TextDirection.ltr),
   ));
 }

dev/manual_tests/lib/focus.dart

@@ -184,8 +184,8 @@ class _FocusDemoState extends State<FocusDemo> {
                         decoration: InputDecoration(labelText: 'Enter Text', filled: true),
                       ),
                     ),
-                    Padding(
-                      padding: const EdgeInsets.all(8.0),
+                    const Padding(
+                      padding: EdgeInsets.all(8.0),
                       child: TextField(
                         decoration: InputDecoration(
                           border: OutlineInputBorder(),

dev/manual_tests/lib/hover.dart

@@ -82,8 +82,8 @@ class _HoverDemoState extends State<HoverDemo> {
                     decoration: InputDecoration(labelText: 'Enter Text', filled: true),
                   ),
                 ),
-                Padding(
-                  padding: const EdgeInsets.all(8.0),
+                const Padding(
+                  padding: EdgeInsets.all(8.0),
                   child: TextField(
                     autofocus: false,
                     decoration: InputDecoration(

examples/flutter_gallery/lib/demo/fortnightly/fortnightly.dart

@@ -139,7 +139,7 @@ class FruitPage extends StatelessWidget {
                       padding: const EdgeInsets.symmetric(vertical: 16),
                       child: Row(
                         children: <Widget>[
-                          CircleAvatar(
+                          const CircleAvatar(
                             backgroundImage: ExactAssetImage(
                               'people/square/trevor.png',
                               package: 'flutter_gallery_assets',

packages/flutter/test/widgets/color_filter_test.dart

@@ -26,8 +26,7 @@ void main() {
   });
 
   testWidgets('Color filter - sepia', (WidgetTester tester) async {
-    // TODO(dnfield): This should be const. https://github.com/dart-lang/sdk/issues/37503
-    final ColorFilter sepia = ColorFilter.matrix(<double>[
+    const ColorFilter sepia = ColorFilter.matrix(<double>[
       0.39,  0.769, 0.189, 0, 0, //
       0.349, 0.686, 0.168, 0, 0, //
       0.272, 0.534, 0.131, 0, 0, //

packages/flutter_driver/test/src/extension_test.dart

@@ -652,10 +652,10 @@ void main() {
     }
 
     await tester.pumpWidget(
-      Directionality(
+      const Directionality(
         textDirection: TextDirection.ltr,
         child: Center(
-            child: const Text('Hello World', key: ValueKey<String>('Text'))
+            child: Text('Hello World', key: ValueKey<String>('Text'))
         ),
       ),
     );