MinimumTextContrastGuideline should dispose image. (#133861)

packages/flutter/test/material/color_scheme_test.dart

@@ -6,6 +6,7 @@ import 'dart:typed_data';
 
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:leak_tracker_flutter_testing/leak_tracker_flutter_testing.dart';
 
 import '../image_data.dart';
 
@@ -443,7 +444,7 @@ void main() {
     );
   });
 
-  testWidgets('generated scheme "on" colors meet a11y contrast guidelines', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('generated scheme "on" colors meet a11y contrast guidelines', (WidgetTester tester) async {
     final ColorScheme colors = ColorScheme.fromSeed(seedColor: Colors.teal);
 
     Widget label(String text, Color textColor, Color background) {

packages/flutter_test/lib/src/accessibility.dart

@@ -329,7 +329,9 @@ class MinimumTextContrastGuideline extends AccessibilityGuideline {
           // the last transform layer.
           final double ratio = 1 / renderView.flutterView.devicePixelRatio;
           image = await layer.toImage(renderView.paintBounds, pixelRatio: ratio);
-          return image.toByteData();
+          final ByteData? data = await image.toByteData();
+          image.dispose();
+          return data;
         },
       );