create media list view controller to handles media list view

packages/stream_chat_flutter/lib/src/media_list_view_controller.dart

@@ -0,0 +1,16 @@
+import 'package:flutter/material.dart';
+
+/// Controller for MediaListView Widget
+class MediaListViewController extends ChangeNotifier {
+  var _shouldUpdateMedia = false;
+
+  /// Getter that knows if the media should be updated.
+  bool get shouldUpdateMedia => _shouldUpdateMedia;
+
+  /// Method that update shouldUpdateMedia and notify all listeners
+  /// about this update.
+  void updateMedia({required bool newValue}) {
+    _shouldUpdateMedia = newValue;
+    notifyListeners();
+  }
+}

packages/stream_chat_flutter/test/src/media_list_view_controller_test.dart

@@ -0,0 +1,37 @@
+import 'package:stream_chat_flutter/src/media_list_view_controller.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('should update media', () {
+    final controller = MediaListViewController();
+
+    expect(controller.shouldUpdateMedia, false);
+
+    controller.updateMedia(newValue: true);
+    expect(controller.shouldUpdateMedia, true);
+
+    controller.dispose();
+  });
+
+  test('should notify listeners on update media', () {
+    final controller = MediaListViewController();
+
+    var callCount = 0;
+    void updateCallsSpy() => callCount++;
+
+    controller.addListener(updateCallsSpy);
+
+    expect(callCount, 0);
+    controller.updateMedia(newValue: false);
+    expect(controller.shouldUpdateMedia, false);
+    expect(callCount, 1);
+
+    controller.updateMedia(newValue: true);
+    expect(controller.shouldUpdateMedia, true);
+    expect(callCount, 2);
+
+    controller
+      ..removeListener(updateCallsSpy)
+      ..dispose();
+  });
+}