[VPAT][A11y][a11y-app] Add a text label to slider. (flutter#177130)

Fix flutter#173008 

Added a visible text label and remove the redundant semantics label.




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Author: hannah-hyj

dev/a11y_assessments/lib/use_cases/slider.dart

@@ -28,7 +28,6 @@ class MainWidget extends StatefulWidget {
 
 class MainWidgetState extends State<MainWidget> {
   double currentSliderValue = 20;
-  static const String accessibilityLabel = 'Accessibility Test Slider';
 
   String pageTitle = getUseCaseName(SliderUseCase());
 
@@ -40,19 +39,22 @@ class MainWidgetState extends State<MainWidget> {
         title: Semantics(headingLevel: 1, child: Text('$pageTitle demo')),
       ),
       body: Center(
-        child: Semantics(
-          label: accessibilityLabel,
-          child: Slider(
-            value: currentSliderValue,
-            max: 100,
-            divisions: 5,
-            label: currentSliderValue.round().toString(),
-            onChanged: (double value) {
-              setState(() {
-                currentSliderValue = value;
-              });
-            },
-          ),
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: <Widget>[
+            const Text('My Slider'),
+            Slider(
+              value: currentSliderValue,
+              max: 100,
+              divisions: 5,
+              label: currentSliderValue.round().toString(),
+              onChanged: (double value) {
+                setState(() {
+                  currentSliderValue = value;
+                });
+              },
+            ),
+          ],
         ),
       ),
     );

dev/a11y_assessments/test/slider_test.dart

@@ -19,10 +19,11 @@ void main() {
     final MainWidgetState state = tester.state<MainWidgetState>(find.byType(MainWidget));
     expect(state.currentSliderValue, 60);
   });
-  testWidgets('slider semantics wrapper exists', (WidgetTester tester) async {
+
+  testWidgets('slider text label exists', (WidgetTester tester) async {
     await pumpsUseCase(tester, SliderUseCase());
-    final Finder semanticsWidget = find.bySemanticsLabel('Accessibility Test Slider');
-    expect(semanticsWidget, findsOneWidget);
+    final Finder labelWidget = find.text('My Slider');
+    expect(labelWidget, findsOneWidget);
   });
 
   testWidgets('slider demo page has one h1 tag', (WidgetTester tester) async {