ImageInfo adds a new getter named sizeBytes to decouple ImageCache and ui.Image (#86555)

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

@@ -411,7 +411,7 @@ class ImageCache {
     void listener(ImageInfo? info, bool syncCall) {
       int? sizeBytes;
       if (info != null) {
-        sizeBytes = info.image.height * info.image.width * 4;
+        sizeBytes = info.sizeBytes;
         info.dispose();
       }
       final _CachedImage image = _CachedImage(

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

@@ -98,6 +98,9 @@ class ImageInfo {
   /// the image.
   final ui.Image image;
 
+  /// The size of raw image pixels in bytes.
+  int get sizeBytes => image.height * image.width * 4;
+
   /// The linear scale factor for drawing this image at its intended size.
   ///
   /// The scale factor applies to the width and the height.

packages/flutter/test/painting/image_info_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 'dart:ui' as ui show Image;
+
+import 'package:flutter/painting.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+Future<void> main() async {
+
+  final ui.Image smallImage = await createTestImage(width: 10, height: 20);
+  final ui.Image middleImage = await createTestImage(width: 20, height: 100);
+  final ui.Image bigImage = await createTestImage(width: 100, height: 200);
+
+  test('ImageInfo sizeBytes', () {
+    ImageInfo imageInfo = ImageInfo(image: smallImage);
+    expect(imageInfo.sizeBytes, equals(800));
+
+    imageInfo = ImageInfo(image: middleImage);
+    expect(imageInfo.sizeBytes, equals(8000));
+
+    imageInfo = ImageInfo(image: bigImage);
+    expect(imageInfo.sizeBytes, equals(80000));
+  });
+}

packages/flutter/test/painting/mocks_for_image_cache.dart

@@ -43,6 +43,9 @@ class TestImageInfo implements ImageInfo {
     image.dispose();
   }
 
+  @override
+  int get sizeBytes => image.height * image.width * 4;
+
   @override
   int get hashCode => hashValues(value, image, scale, debugLabel);