a11y: Exclude children of nested keyboard accessible controls from a11y tree.

ui/views/widget/native_widget_mac_accessibility_unittest.mm

Index: ui/views/widget/native_widget_mac_accessibility_unittest.mm
diff --git a/ui/views/widget/native_widget_mac_accessibility_unittest.mm b/ui/views/widget/native_widget_mac_accessibility_unittest.mm
index 3d641d190f9eab41fa0d4a97d726766736902263..0b1cd3985695bfe35bc1dc243a46a1936ea830c4 100644
--- a/ui/views/widget/native_widget_mac_accessibility_unittest.mm
+++ b/ui/views/widget/native_widget_mac_accessibility_unittest.mm
@@ -14,6 +14,7 @@
 #import "ui/accessibility/platform/ax_platform_node_mac.h"
 #include "ui/base/ime/text_input_type.h"
 #import "ui/gfx/mac/coordinate_conversion.h"
+#include "ui/views/controls/button/label_button.h"
 #include "ui/views/controls/label.h"
 #include "ui/views/controls/textfield/textfield.h"
 #include "ui/views/test/widget_test.h"
@@ -102,6 +103,22 @@ class NativeWidgetMacAccessibilityTest : public test::WidgetTest {
 
 }  // namespace
 
+// Check that potentially keyboard-focusable elements are always leaf nodes.
+TEST_F(NativeWidgetMacAccessibilityTest, FocusableElementsAreLeafNodes) {
+  // LabelButtons will have a label inside the button. The label should be
+  // ignored because the button is potentially keyboard focusable.
+  LabelButton* button =
+      new LabelButton(nullptr, base::SysNSStringToUTF16(kTestStringValue));
+  button->SetSize(widget()->GetContentsView()->size());
+  widget()->GetContentsView()->AddChildView(button);
+  EXPECT_NSEQ(NSAccessibilityButtonRole,
+              AttributeValueAtMidpoint(NSAccessibilityRoleAttribute));
+  EXPECT_EQ(
+      0u,
+      [[button->GetNativeViewAccessible()
+          accessibilityAttributeValue:NSAccessibilityChildrenAttribute] count]);
+}
+
 // Test for NSAccessibilityChildrenAttribute, and ensure it excludes ignored
 // children from the accessibility tree.
 TEST_F(NativeWidgetMacAccessibilityTest, ChildrenAttribute) {