Mac a11y: Add Help, TopLevelUIElement, and Window accessibility attributes.

ui/accessibility/platform/ax_platform_node_mac.mm

Index: ui/accessibility/platform/ax_platform_node_mac.mm
diff --git a/ui/accessibility/platform/ax_platform_node_mac.mm b/ui/accessibility/platform/ax_platform_node_mac.mm
index 346cb7168571392f59d609106ff894c08bd0b7d8..8ce10097f5bbffe96b3c3a98f013ef356e5d321b 100644
--- a/ui/accessibility/platform/ax_platform_node_mac.mm
+++ b/ui/accessibility/platform/ax_platform_node_mac.mm
@@ -305,6 +305,9 @@ void NotifyMacEvent(NSView* target, ui::AXEvent event_type) {
     NSAccessibilityRoleDescriptionAttribute,
     NSAccessibilityEnabledAttribute,
     NSAccessibilityFocusedAttribute,
+    NSAccessibilityHelpAttribute,
+    NSAccessibilityTopLevelUIElementAttribute,
+    NSAccessibilityWindowAttribute,
   ];
 
   // Attributes required for user-editable controls.
@@ -432,6 +435,18 @@ void NotifyMacEvent(NSView* target, ui::AXEvent event_type) {
   return [NSNumber numberWithBool:NO];
 }
 
+- (NSString*)AXHelp {
+  return [self getStringAttribute:ui::AX_ATTR_HELP_TEXT];
+}
+
+- (NSWindow*)AXTopLevelUIElement {
+  return [self AXWindow];
+}
+
+- (NSWindow*)AXWindow {
+  return node_->GetDelegate()->GetTopLevelWidget();
+}
+
 // Textfield-specific NSAccessibility attributes.
 
 - (NSNumber*)AXInsertionPointLineNumber {