A treegrid should expose its rows in MSAA/IA2 as outlineitems.

content/browser/accessibility/browser_accessibility_win.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_WIN_H_
 #define CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_WIN_H_
 
 #include <atlbase.h>
 #include <atlcom.h>
 #include <oleacc.h>
@@ skipping 902 matching lines @@
                                 int target_id);
 
   // Updates object attributes of IA2 with html attributes.
   void UpdateRequiredAttributes();
 
   // Fire a Windows-specific accessibility event notification on this node.
   void FireNativeEvent(LONG win_event_type) const;
 
   ui::AXPlatformNodeWin* GetPlatformNodeWin() const;
 
+  static bool IsInTreeGrid(const BrowserAccessibility* item);

[aleventhal, 2017/04/12 15:36:31]

Not sure if better as static, or does it not really matter?

+
   struct WinAttributes {
     WinAttributes();
     ~WinAttributes();
 
     // IAccessible role and state.
     int32_t ia_role;
     int32_t ia_state;
     base::string16 role_name;
 
     // IAccessible name, description, help, value.
@@ skipping 47 matching lines @@
 
 CONTENT_EXPORT BrowserAccessibilityWin*
 ToBrowserAccessibilityWin(BrowserAccessibility* obj);
 
 CONTENT_EXPORT const BrowserAccessibilityWin*
 ToBrowserAccessibilityWin(const BrowserAccessibility* obj);
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_ACCESSIBILITY_BROWSER_ACCESSIBILITY_WIN_H_