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

ui/accessibility/platform/ax_platform_node_delegate.h

Index: ui/accessibility/platform/ax_platform_node_delegate.h
diff --git a/ui/accessibility/platform/ax_platform_node_delegate.h b/ui/accessibility/platform/ax_platform_node_delegate.h
index e6dd24d90413fa1db79d36d6d01477807d2282cf..a46e3873936ca49588b2e942d9034610eee4a8a1 100644
--- a/ui/accessibility/platform/ax_platform_node_delegate.h
+++ b/ui/accessibility/platform/ax_platform_node_delegate.h
@@ -35,6 +35,9 @@ class AX_EXPORT AXPlatformNodeDelegate {
   // is mostly to implement support for walking the accessibility tree.
   virtual const AXNodeData& GetData() = 0;
 
+  // Get the window the node is contained in.
+  virtual gfx::NativeWindow GetTopLevelWidget() = 0;
+
   // Get the parent of the node, which may be an AXPlatformNode or it may
   // be a native accessible object implemented by another class.
   virtual gfx::NativeViewAccessible GetParent() = 0;