Add asset manifest parsing benchmark (#112836)

dev/benchmarks/microbenchmarks/lib/foundation/decode_and_parse_asset_manifest.dart

@@ -0,0 +1,42 @@
+// 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 'dart:convert';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart' show PlatformAssetBundle;
+import 'package:flutter/widgets.dart';
+
+import '../common.dart';
+
+const int _kNumIterations = 1000;
+
+void main() async {
+  assert(false, "Don't run benchmarks in debug mode! Use 'flutter run --release'.");
+
+  final BenchmarkResultPrinter printer = BenchmarkResultPrinter();
+  WidgetsFlutterBinding.ensureInitialized();
+  final Stopwatch watch = Stopwatch();
+  final PlatformAssetBundle bundle = PlatformAssetBundle();
+
+  final ByteData assetManifestBytes = await bundle.load('money_asset_manifest.json');
+  watch.start();
+  for (int i = 0; i < _kNumIterations; i++) {
+    bundle.clear();
+    final String json = utf8.decode(assetManifestBytes.buffer.asUint8List());
+    // This is a test, so we don't need to worry about this rule.
+    // ignore: invalid_use_of_visible_for_testing_member
+    await AssetImage.manifestParser(json);
+  }
+  watch.stop();
+
+  printer.addResult(
+    description: 'Load and Parse Large Asset Manifest',
+    value: watch.elapsedMilliseconds.toDouble(),
+    unit: 'ms',
+    name: 'load_and_parse_large_asset_manifest',
+  );
+
+  printer.printToStdout();
+}

dev/benchmarks/microbenchmarks/pubspec.yaml

@@ -70,6 +70,7 @@ dependencies:
 flutter:
   uses-material-design: true
   assets:
+    - money_asset_manifest.json
     - packages/flutter_gallery_assets/people/ali_landscape.png
     - packages/flutter_gallery_assets/monochrome/red-square-1024x1024.png
     - packages/flutter_gallery_assets/logos/flutter_white/logo.png

dev/devicelab/lib/tasks/microbenchmarks.dart

@@ -57,6 +57,7 @@ TaskFunction createMicrobenchmarkTask({bool enableImpeller = false}) {
       ...await runMicrobench('lib/foundation/standard_message_codec_bench.dart'),
       ...await runMicrobench('lib/foundation/standard_method_codec_bench.dart'),
       ...await runMicrobench('lib/foundation/timeline_bench.dart'),
+      ...await runMicrobench('lib/foundation/decode_and_parse_asset_manifest.dart'),
       ...await runMicrobench('lib/geometry/matrix_utils_transform_bench.dart'),
       ...await runMicrobench('lib/geometry/rrect_contains_bench.dart'),
       ...await runMicrobench('lib/gestures/gesture_detector_bench.dart'),

packages/flutter/lib/src/painting/image_resolution.dart

@@ -284,7 +284,7 @@ class AssetImage extends AssetBundleImageProvider {
     Completer<AssetBundleImageKey>? completer;
     Future<AssetBundleImageKey>? result;
 
-    chosenBundle.loadStructuredData<Map<String, List<String>>?>(_kAssetManifestFileName, _manifestParser).then<void>(
+    chosenBundle.loadStructuredData<Map<String, List<String>>?>(_kAssetManifestFileName, manifestParser).then<void>(
       (Map<String, List<String>>? manifest) {
         final String chosenName = _chooseVariant(
           keyName,
@@ -328,7 +328,9 @@ class AssetImage extends AssetBundleImageProvider {
     return completer.future;
   }
 
-  static Future<Map<String, List<String>>?> _manifestParser(String? jsonData) {
+  /// Parses the asset manifest string into a strongly-typed map.
+  @visibleForTesting
+  static Future<Map<String, List<String>>?> manifestParser(String? jsonData) {
     if (jsonData == null) {
       return SynchronousFuture<Map<String, List<String>>?>(null);
     }