[web_ui] Fixed aria-live attribute on web (flutter#27985)

* Fixed aria-live attribute on web

AUTHORS

@@ -20,3 +20,4 @@ Hidenori Matsubayashi <[email protected]>
 Sarbagya Dhaubanjar <[email protected]>
 Callum Moffat <[email protected]>
 Koutaro Mori <[email protected]>
+TheOneWithTheBraid <[email protected]>

lib/web_ui/lib/src/engine/semantics/semantics_helper.dart

@@ -174,7 +174,8 @@ class DesktopSemanticsEnabler extends SemanticsEnabler {
 
   @override
   html.Element prepareAccessibilityPlaceholder() {
-    final html.Element placeholder = _semanticsPlaceholder = html.Element.tag('flt-semantics-placeholder');
+    final html.Element placeholder =
+        _semanticsPlaceholder = html.Element.tag('flt-semantics-placeholder');
 
     // Only listen to "click" because other kinds of events are reported via
     // PointerBinding.
@@ -189,7 +190,7 @@ class DesktopSemanticsEnabler extends SemanticsEnabler {
     // to the assistive technology user.
     placeholder
       ..setAttribute('role', 'button')
-      ..setAttribute('aria-live', 'true')
+      ..setAttribute('aria-live', 'polite')
       ..setAttribute('tabindex', '0')
       ..setAttribute('aria-label', placeholderMessage);
 
@@ -372,7 +373,8 @@ class MobileSemanticsEnabler extends SemanticsEnabler {
 
   @override
   html.Element prepareAccessibilityPlaceholder() {
-    final html.Element placeholder = _semanticsPlaceholder = html.Element.tag('flt-semantics-placeholder');
+    final html.Element placeholder =
+        _semanticsPlaceholder = html.Element.tag('flt-semantics-placeholder');
 
     // Only listen to "click" because other kinds of events are reported via
     // PointerBinding.

lib/web_ui/test/engine/semantics/semantics_helper_test.dart

@@ -35,9 +35,9 @@ void testMain() {
       EngineSemanticsOwner.instance.semanticsEnabled = false;
     });
 
-    test('prepare accesibility placeholder', () async {
+    test('prepare accessibility placeholder', () async {
       expect(_placeholder!.getAttribute('role'), 'button');
-      expect(_placeholder!.getAttribute('aria-live'), 'true');
+      expect(_placeholder!.getAttribute('aria-live'), 'polite');
       expect(_placeholder!.getAttribute('tabindex'), '0');
 
       html.document.body!.append(_placeholder!);
@@ -72,7 +72,7 @@ void testMain() {
     });
 
     test(
-        'Relevants events targeting placeholder should not be forwarded to the framework',
+        'Relevant events targeting placeholder should not be forwarded to the framework',
         () async {
       final html.Event event = html.MouseEvent('mousedown');
       _placeholder!.dispatchEvent(event);
@@ -110,15 +110,15 @@ void testMain() {
         EngineSemanticsOwner.instance.semanticsEnabled = false;
       });
 
-      test('prepare accesibility placeholder', () async {
+      test('prepare accessibility placeholder', () async {
         expect(_placeholder!.getAttribute('role'), 'button');
 
         // Placeholder should cover all the screen on a mobile device.
         final num bodyHeight = html.window.innerHeight!;
-        final num bodyWidht = html.window.innerWidth!;
+        final num bodyWidth = html.window.innerWidth!;
 
         expect(_placeholder!.getBoundingClientRect().height, bodyHeight);
-        expect(_placeholder!.getBoundingClientRect().width, bodyWidht);
+        expect(_placeholder!.getBoundingClientRect().width, bodyWidth);
       });
 
       test('Non-relevant events should be forwarded to the framework',