Added new constructor RefreshIndicator.noSpinner() (#152075)

This PR adds a new constructor to the RefreshIndicator's class, which is `noSpinner`.
The purpose of this new constructor is to create a RefreshIndicator that doesn't show a spinner when the user arms it by pulling.

The work is based on a partial that is here: https://github.com/flutter/flutter/pull/133507

I addressed the following issues reported in the PR above:
- in the example for `noSpinner`, arming the RefreshIndicator now shows a CircularProgressIndicator, instead of just printing text to the console;
- added a test for the new example;
- added a doc comment on the new constructor;

Fixes https://github.com/flutter/flutter/issues/132775

examples/api/lib/material/refresh_indicator/refresh_indicator.2.dart

@@ -0,0 +1,95 @@
+// Copyright 2014 The Flutter 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 'package:flutter/material.dart';
+
+/// Flutter code sample for [RefreshIndicator.noSpinner].
+
+void main() => runApp(const RefreshIndicatorExampleApp());
+
+class RefreshIndicatorExampleApp extends StatelessWidget {
+  const RefreshIndicatorExampleApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return const MaterialApp(
+      home: RefreshIndicatorExample(),
+    );
+  }
+}
+
+class RefreshIndicatorExample extends StatefulWidget {
+  const RefreshIndicatorExample({super.key});
+
+  @override
+  State<RefreshIndicatorExample> createState() => _RefreshIndicatorExampleState();
+}
+
+class _RefreshIndicatorExampleState extends State<RefreshIndicatorExample> {
+  bool _isRefreshing = false;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text('RefreshIndicator.noSpinner Sample'),
+      ),
+      body: Stack(
+        children: <Widget>[
+          RefreshIndicator.noSpinner(
+            // Callback function used by the app to listen to the
+            // status of the RefreshIndicator pull-down action.
+            onStatusChange: (RefreshIndicatorStatus? status) {
+              if (status == RefreshIndicatorStatus.done) {
+                setState(() {
+                  _isRefreshing = false;
+                });
+              }
+            },
+
+            // Callback that gets called whenever the user pulls down to refresh.
+            onRefresh: () async {
+              // This can be also done in onStatusChange when the status is RefreshIndicatorStatus.refresh.
+              setState(() {
+                _isRefreshing = true;
+              });
+
+              // Replace this delay with the code to be executed during refresh
+              // and return asynchronous code.
+              return Future<void>.delayed(const Duration(seconds: 3));
+            },
+
+            child: CustomScrollView(
+              slivers: <Widget>[
+                SliverList.builder(
+                  itemCount: 20,
+                  itemBuilder: (BuildContext context, int index) {
+                    return ListTile(
+                      tileColor: Colors.green[100],
+                      title: const Text('Pull down here'),
+                      subtitle: const Text('A custom refresh indicator will be shown'),
+                    );
+                  }
+                )
+              ],
+            ),
+          ),
+
+          // Shows an overlay with a CircularProgressIndicator when refreshing.
+          if (_isRefreshing)
+            ColoredBox(
+              color: Colors.black45,
+              child: Align(
+                child: CircularProgressIndicator(
+                  color: Colors.purple[500],
+                  strokeWidth: 10,
+                  semanticsLabel: 'Circular progress indicator',
+                ),
+              ),
+            ),
+        ]
+      ),
+    );
+  }
+}

examples/api/test/material/refresh_indicator/refresh_indicator.2_test.dart

@@ -0,0 +1,26 @@
+// Copyright 2014 The Flutter 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 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/refresh_indicator/refresh_indicator.2.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Pulling from scroll view triggers a refresh indicator which shows a CircularProgressIndicator', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.RefreshIndicatorExampleApp(),
+    );
+
+    // Pull the first item.
+    await tester.fling(find.text('Pull down here').first, const Offset(0.0, 300.0), 1000.0);
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+    await tester.pump(const Duration(seconds: 1));
+
+    expect(find.byType(RefreshProgressIndicator), findsNothing);
+    expect(find.bySemanticsLabel('Circular progress indicator'), findsOneWidget);
+
+    await tester.pumpAndSettle(); // Advance pending time.
+  });
+}