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

ui/accessibility/ax_view_state.h

Index: ui/accessibility/ax_view_state.h
diff --git a/ui/accessibility/ax_view_state.h b/ui/accessibility/ax_view_state.h
index 46e55f89cabed8ddff24ef7630db2f59e7ed64b2..088a63ba2412069123df6a93ea9bcf9ce2c096ec 100644
--- a/ui/accessibility/ax_view_state.h
+++ b/ui/accessibility/ax_view_state.h
@@ -57,6 +57,9 @@ struct AX_EXPORT AXViewState {
   // The view's placeholder value, used only for views with editable text.
   base::string16 placeholder;
 
+  // The view's help text, set to the view's tooltip text (if any).
+  base::string16 help_text;
+
   // The selection start and end. Only applies to views with text content,
   // such as a text box or combo box; start and end should be -1 otherwise.
   int selection_start;