Created method to report ImageChunkEvents (#55044)

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

@@ -516,6 +516,23 @@ abstract class ImageStreamCompleter with Diagnosticable {
     }
   }
 
+  /// Calls all the registered [ImageChunkListener]s (listeners with an
+  /// [ImageStreamListener.onChunk] specified) to notify them of a new
+  /// [ImageChunkEvent].
+  @protected
+  void reportImageChunkEvent(ImageChunkEvent event){
+    if (hasListeners) {
+      // Make a copy to allow for concurrent modification.
+      final List<ImageChunkListener> localListeners = _listeners
+          .map<ImageChunkListener>((ImageStreamListener listener) => listener.onChunk)
+          .where((ImageChunkListener chunkListener) => chunkListener != null)
+          .toList();
+      for (final ImageChunkListener listener in localListeners) {
+        listener(event);
+      }
+    }
+  }
+
   /// Accumulates a list of strings describing the object's state. Subclasses
   /// should override this to have their information included in [toString].
   @override
@@ -626,19 +643,8 @@ class MultiFrameImageStreamCompleter extends ImageStreamCompleter {
       );
     });
     if (chunkEvents != null) {
-      chunkEvents.listen(
-        (ImageChunkEvent event) {
-          if (hasListeners) {
-            // Make a copy to allow for concurrent modification.
-            final List<ImageChunkListener> localListeners = _listeners
-                .map<ImageChunkListener>((ImageStreamListener listener) => listener.onChunk)
-                .where((ImageChunkListener chunkListener) => chunkListener != null)
-                .toList();
-            for (final ImageChunkListener listener in localListeners) {
-              listener(event);
-            }
-          }
-        }, onError: (dynamic error, StackTrace stack) {
+      chunkEvents.listen(reportImageChunkEvent,
+        onError: (dynamic error, StackTrace stack) {
           reportError(
             context: ErrorDescription('loading an image'),
             exception: error,

packages/flutter/test/painting/image_stream_test.dart

@@ -78,6 +78,17 @@ class MockCodec implements Codec {
 
 }
 
+class FakeEventReportingImageStreamCompleter extends ImageStreamCompleter {
+  FakeEventReportingImageStreamCompleter({Stream<ImageChunkEvent> chunkEvents,}) {
+    if (chunkEvents != null) {
+      chunkEvents.listen((ImageChunkEvent event) {
+          reportImageChunkEvent(event);
+        },
+      );
+    }
+  }
+}
+
 void main() {
   testWidgets('Codec future fails', (WidgetTester tester) async {
     final Completer<Codec> completer = Completer<Codec>();
@@ -128,7 +139,54 @@ void main() {
     expect(mockCodec.numFramesAsked, 1);
   });
 
-  testWidgets('Chunk events are delivered', (WidgetTester tester) async {
+  testWidgets('Chunk events of base ImageStreamCompleter are delivered', (WidgetTester tester) async {
+    final List<ImageChunkEvent> chunkEvents = <ImageChunkEvent>[];
+    final StreamController<ImageChunkEvent> streamController = StreamController<ImageChunkEvent>();
+    final ImageStreamCompleter imageStream = FakeEventReportingImageStreamCompleter(
+      chunkEvents: streamController.stream,
+    );
+
+    imageStream.addListener(ImageStreamListener(
+      (ImageInfo image, bool synchronousCall) { },
+      onChunk: (ImageChunkEvent event) {
+        chunkEvents.add(event);
+      },
+    ));
+    streamController.add(const ImageChunkEvent(cumulativeBytesLoaded: 1, expectedTotalBytes: 3));
+    streamController.add(const ImageChunkEvent(cumulativeBytesLoaded: 2, expectedTotalBytes: 3));
+    await tester.idle();
+
+    expect(chunkEvents.length, 2);
+    expect(chunkEvents[0].cumulativeBytesLoaded, 1);
+    expect(chunkEvents[0].expectedTotalBytes, 3);
+    expect(chunkEvents[1].cumulativeBytesLoaded, 2);
+    expect(chunkEvents[1].expectedTotalBytes, 3);
+  });
+
+  testWidgets('Chunk events of base ImageStreamCompleter are not buffered before listener registration', (WidgetTester tester) async {
+    final List<ImageChunkEvent> chunkEvents = <ImageChunkEvent>[];
+    final StreamController<ImageChunkEvent> streamController = StreamController<ImageChunkEvent>();
+    final ImageStreamCompleter imageStream = FakeEventReportingImageStreamCompleter(
+      chunkEvents: streamController.stream,
+    );
+
+    streamController.add(const ImageChunkEvent(cumulativeBytesLoaded: 1, expectedTotalBytes: 3));
+    await tester.idle();
+    imageStream.addListener(ImageStreamListener(
+      (ImageInfo image, bool synchronousCall) { },
+      onChunk: (ImageChunkEvent event) {
+        chunkEvents.add(event);
+      },
+    ));
+    streamController.add(const ImageChunkEvent(cumulativeBytesLoaded: 2, expectedTotalBytes: 3));
+    await tester.idle();
+
+    expect(chunkEvents.length, 1);
+    expect(chunkEvents[0].cumulativeBytesLoaded, 2);
+    expect(chunkEvents[0].expectedTotalBytes, 3);
+  });
+
+  testWidgets('Chunk events of MultiFrameImageStreamCompleter are delivered', (WidgetTester tester) async {
     final List<ImageChunkEvent> chunkEvents = <ImageChunkEvent>[];
     final Completer<Codec> completer = Completer<Codec>();
     final StreamController<ImageChunkEvent> streamController = StreamController<ImageChunkEvent>();
@@ -155,7 +213,7 @@ void main() {
     expect(chunkEvents[1].expectedTotalBytes, 3);
   });
 
-  testWidgets('Chunk events are not buffered before listener registration', (WidgetTester tester) async {
+  testWidgets('Chunk events of MultiFrameImageStreamCompleter are not buffered before listener registration', (WidgetTester tester) async {
     final List<ImageChunkEvent> chunkEvents = <ImageChunkEvent>[];
     final Completer<Codec> completer = Completer<Codec>();
     final StreamController<ImageChunkEvent> streamController = StreamController<ImageChunkEvent>();