Revert "Load assets in flutter_test without turning event loop. (#115123)" (#115156)

This reverts commit 88e49ed2.

packages/flutter/lib/src/foundation/synchronous_future.dart

@@ -38,11 +38,11 @@ class SynchronousFuture<T> implements Future<T> {
 
   @override
   Future<R> then<R>(FutureOr<R> Function(T value) onValue, { Function? onError }) {
-    final FutureOr<R> result = onValue(_value);
+    final dynamic result = onValue(_value);
     if (result is Future<R>) {
       return result;
     }
-    return SynchronousFuture<R>(result);
+    return SynchronousFuture<R>(result as R);
   }
 
   @override

packages/flutter/lib/src/services/asset_bundle.dart

@@ -247,9 +247,10 @@ abstract class CachingAssetBundle extends AssetBundle {
 /// An [AssetBundle] that loads resources using platform messages.
 class PlatformAssetBundle extends CachingAssetBundle {
   @override
-  Future<ByteData> load(String key) {
+  Future<ByteData> load(String key) async {
     final Uint8List encoded = utf8.encoder.convert(Uri(path: Uri.encodeFull(key)).path);
-    final Future<ByteData>? future = ServicesBinding.instance.defaultBinaryMessenger.send('flutter/assets', encoded.buffer.asByteData())?.then((ByteData? asset) {
+    final ByteData? asset =
+        await ServicesBinding.instance.defaultBinaryMessenger.send('flutter/assets', encoded.buffer.asByteData());
     if (asset == null) {
       throw FlutterError.fromParts(<DiagnosticsNode>[
         _errorSummaryWithKey(key),
@@ -257,14 +258,6 @@ class PlatformAssetBundle extends CachingAssetBundle {
       ]);
     }
     return asset;
-    });
-    if (future == null) {
-      throw FlutterError.fromParts(<DiagnosticsNode>[
-          _errorSummaryWithKey(key),
-          ErrorDescription('The asset does not exist or has empty data.'),
-        ]);
-    }
-    return future;
   }
 
   @override

packages/flutter_test/lib/src/_binding_io.dart

@@ -6,8 +6,8 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
-import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
 import 'package:path/path.dart' as path;
 // ignore: deprecated_member_use
 import 'package:test_api/test_api.dart' as test_package;
@@ -42,7 +42,7 @@ void mockFlutterAssets() {
   /// platform messages.
   SystemChannels.navigation.setMockMethodCallHandler((MethodCall methodCall) async {});
 
-  ServicesBinding.instance.defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData? message) {
+  ServicesBinding.instance.defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData? message) async {
     assert(message != null);
     String key = utf8.decode(message!.buffer.asUint8List());
     File asset = File(path.join(assetFolderPath, key));
@@ -62,7 +62,7 @@ void mockFlutterAssets() {
     }
 
     final Uint8List encoded = Uint8List.fromList(asset.readAsBytesSync());
-    return SynchronousFuture<ByteData>(encoded.buffer.asByteData());
+    return Future<ByteData>.value(encoded.buffer.asByteData());
   });
 }
 

packages/flutter_test/test/bindings_test.dart

@@ -10,7 +10,6 @@
 import 'dart:async';
 import 'dart:io';
 
-import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -91,13 +90,4 @@ void main() {
       binding.idle();
     });
   });
-
-  testWidgets('Assets in the tester can be loaded without turning event loop', (WidgetTester tester) async {
-    bool responded = false;
-    // The particular asset does not matter, as long as it exists.
-    rootBundle.load('AssetManifest.json').then((ByteData data) {
-      responded = true;
-    });
-    expect(responded, true);
-  });
 }