Hides the scroll bar from UIScrollView (flutter#27214)

* Hides the scroll bar from UIScrollView

* fix test

Author: chunhtai

shell/platform/darwin/ios/framework/Source/SemanticsObject.mm

@@ -153,6 +153,8 @@ - (instancetype)initWithSemanticsObject:(SemanticsObject*)semanticsObject {
   if (self) {
     _semanticsObject = [semanticsObject retain];
     [semanticsObject.bridge->view() addSubview:self];
+    [self setShowsHorizontalScrollIndicator:NO];
+    [self setShowsVerticalScrollIndicator:NO];
   }
   return self;
 }

shell/platform/darwin/ios/framework/Source/SemanticsObjectTest.mm

@@ -370,6 +370,28 @@ - (void)testFlutterScrollableSemanticsObjectIsHiddenWhenVoiceOverIsRunning {
   XCTAssertFalse(scrollable_object.isAccessibilityElement);
 }
 
+- (void)testFlutterScrollableSemanticsObjectHidesScrollBar {
+  fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(
+      new flutter::MockAccessibilityBridge());
+  fml::WeakPtr<flutter::AccessibilityBridgeIos> bridge = factory.GetWeakPtr();
+
+  flutter::SemanticsNode node;
+  node.flags = static_cast<int32_t>(flutter::SemanticsFlags::kHasImplicitScrolling);
+  node.actions = flutter::kHorizontalScrollSemanticsActions;
+  node.rect = SkRect::MakeXYWH(0, 0, 100, 200);
+  node.scrollExtentMax = 100.0;
+  node.scrollPosition = 0.0;
+
+  FlutterSemanticsObject* delegate = [[FlutterSemanticsObject alloc] initWithBridge:bridge uid:0];
+  FlutterScrollableSemanticsObject* scrollable =
+      [[FlutterScrollableSemanticsObject alloc] initWithSemanticsObject:delegate];
+  SemanticsObject* scrollable_object = static_cast<SemanticsObject*>(scrollable);
+  [scrollable_object setSemanticsNode:&node];
+  [scrollable_object accessibilityBridgeDidFinishUpdate];
+  XCTAssertFalse(scrollable.showsHorizontalScrollIndicator);
+  XCTAssertFalse(scrollable.showsVerticalScrollIndicator);
+}
+
 - (void)testSemanticsObjectBuildsAttributedString {
   fml::WeakPtrFactory<flutter::AccessibilityBridgeIos> factory(
       new flutter::MockAccessibilityBridge());