Update rendering smoke tests to assert a frame has been scheduled (#82963)

examples/layers/rendering/custom_coordinate_systems.dart

@@ -21,5 +21,5 @@ RenderBox buildSectorExample() {
 }
 
 void main() {
-  RenderingFlutterBinding(root: buildSectorExample());
+  RenderingFlutterBinding(root: buildSectorExample()).scheduleFrame();
 }

examples/layers/rendering/flex_layout.dart

@@ -86,5 +86,5 @@ void main() {
     child: RenderPadding(child: table, padding: const EdgeInsets.symmetric(vertical: 50.0)),
   );
 
-  RenderingFlutterBinding(root: root);
+  RenderingFlutterBinding(root: root).scheduleFrame();
 }

examples/layers/rendering/hello_world.dart

@@ -25,5 +25,5 @@ void main() {
         textDirection: TextDirection.ltr,
       ),
     ),
-  );
+  ).scheduleFrame();
 }

examples/layers/rendering/touch_input.dart

@@ -132,5 +132,5 @@ void main() {
     ..left = 20.0;
 
   // Finally, we attach the render tree we've built to the screen.
-  RenderingFlutterBinding(root: stack);
+  RenderingFlutterBinding(root: stack).scheduleFrame();
 }

examples/layers/test/smoketests/rendering/custom_coordinate_systems_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
+import 'package:flutter/scheduler.dart';
 // ignore: deprecated_member_use
 import 'package:test_api/test_api.dart' hide TypeMatcher, isInstanceOf;
 
@@ -12,5 +13,6 @@ void main() {
   test('layers smoketest for rendering/custom_coordinate_systems.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
+    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/flex_layout_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
+import 'package:flutter/scheduler.dart';
 // ignore: deprecated_member_use
 import 'package:test_api/test_api.dart' hide TypeMatcher, isInstanceOf;
 
@@ -12,5 +13,6 @@ void main() {
   test('layers smoketest for rendering/flex_layout.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
+    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/hello_world_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
+import 'package:flutter/scheduler.dart';
 // ignore: deprecated_member_use
 import 'package:test_api/test_api.dart' hide TypeMatcher, isInstanceOf;
 
@@ -12,5 +13,6 @@ void main() {
   test('layers smoketest for rendering/hello_world.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
+    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/spinning_square_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
+import 'package:flutter/scheduler.dart';
 // ignore: deprecated_member_use
 import 'package:test_api/test_api.dart' hide TypeMatcher, isInstanceOf;
 
@@ -12,5 +13,6 @@ void main() {
   test('layers smoketest for rendering/spinning_square.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
+    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
   });
 }

examples/layers/test/smoketests/rendering/touch_input_test.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
+import 'package:flutter/scheduler.dart';
 // ignore: deprecated_member_use
 import 'package:test_api/test_api.dart' hide TypeMatcher, isInstanceOf;
 
@@ -12,5 +13,6 @@ void main() {
   test('layers smoketest for rendering/touch_input.dart', () {
     FlutterError.onError = (FlutterErrorDetails details) { throw details.exception; };
     demo.main();
+    expect(SchedulerBinding.instance!.hasScheduledFrame, true);
   });
 }

packages/flutter/lib/src/rendering/binding.dart

@@ -534,6 +534,9 @@ class RenderingFlutterBinding extends BindingBase with GestureBinding, Scheduler
   ///
   /// The `root` render box is attached directly to the [renderView] and is
   /// given constraints that require it to fill the window.
+  ///
+  /// This binding does not automatically schedule any frames. Callers are
+  /// responsible for deciding when to first call [scheduleFrame].
   RenderingFlutterBinding({ RenderBox? root }) {
     assert(renderView != null);
     renderView.child = root;