anchor.diff:      try {
         sceneElement.append(engineCanvas.rootElement);
         html.document.body.append(sceneElement);
  -      await matchGoldenFile('$fileName.png', region: region, maxDiffRatePercent: 0.0);
  +      await matchGoldenFile('$fileName.png', region: region, maxDiffRatePercent: maxDiffRatePercent);
       } finally {
         // The page is reused across tests, so remove the element after taking the
         // Scuba screenshot.
  
positive.code:     rc.drawImage(createTestImage(), Offset(135.0, 130.0),
          Paint()..blendMode = BlendMode.multiply);
      rc.restore();
      await _checkScreenshot(rc, 'canvas_blend_image_multiply');
    });
  }
  
  
negative.code: 
    // Commit a recording canvas to a bitmap, and compare with the expected
    Future<void> _checkScreenshot(RecordingCanvas rc, String fileName,
        {Rect region = const Rect.fromLTWH(0, 0, 500, 500),
         double maxDiffRatePercent = 0.0}) async {
      final EngineCanvas engineCanvas = BitmapCanvas(screenRect);
  
      rc.apply(engineCanvas);
  