Specify ifTrue and ifFalse for strut FlagProperty (#40609)

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

@@ -597,7 +597,7 @@ class StrutStyle extends Diagnosticable {
     ));
     styles.add(EnumProperty<FontStyle>('${prefix}style', fontStyle, defaultValue: null));
     styles.add(DoubleProperty('${prefix}height', height, unit: 'x', defaultValue: null));
-    styles.add(FlagProperty('${prefix}forceStrutHeight', value: forceStrutHeight, defaultValue: null));
+    styles.add(FlagProperty('${prefix}forceStrutHeight', value: forceStrutHeight, defaultValue: null, ifTrue: '$prefix<strut height forced>', ifFalse: '$prefix<strut height normal>'));
 
     final bool styleSpecified = styles.any((DiagnosticsNode n) => !n.isFiltered(DiagnosticLevel.info));
     styles.forEach(properties.add);

packages/flutter/test/painting/strut_style_test.dart

+// Copyright 2016 The Chromium 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 'package:flutter/painting.dart';
+import '../flutter_test_alternative.dart';
+
+void main() {
+  test('StrutStyle diagnostics test', () {
+    const StrutStyle s0 = StrutStyle(
+      fontFamily: 'Serif',
+      fontSize: 14,
+    );
+    expect(
+      s0.toString(),
+      equals('StrutStyle(family: Serif, size: 14.0)'),
+    );
+
+    const StrutStyle s1 = StrutStyle(
+      fontFamily: 'Serif',
+      fontSize: 14,
+      forceStrutHeight: true,
+    );
+    expect(s1.fontFamily, 'Serif');
+    expect(s1.fontSize, 14.0);
+    expect(s1, equals(s1));
+    expect(
+      s1.toString(),
+      equals('StrutStyle(family: Serif, size: 14.0, <strut height forced>)'),
+    );
+
+    const StrutStyle s2 = StrutStyle(
+      fontFamily: 'Serif',
+      fontSize: 14,
+      forceStrutHeight: false,
+    );
+    expect(
+      s2.toString(),
+      equals('StrutStyle(family: Serif, size: 14.0, <strut height normal>)'),
+    );
+
+    const StrutStyle s3 = StrutStyle();
+    expect(
+      s3.toString(),
+      equals('StrutStyle'),
+    );
+
+    const StrutStyle s4 = StrutStyle(
+      forceStrutHeight: false,
+    );
+    expect(
+      s4.toString(),
+      equals('StrutStyle(<strut height normal>)'),
+    );
+
+    const StrutStyle s5 = StrutStyle(
+      forceStrutHeight: true,
+    );
+    expect(
+      s5.toString(),
+      equals('StrutStyle(<strut height forced>)'),
+    );
+  });
+}