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

content/browser/accessibility/browser_accessibility_win.cc

Index: content/browser/accessibility/browser_accessibility_win.cc
diff --git a/content/browser/accessibility/browser_accessibility_win.cc b/content/browser/accessibility/browser_accessibility_win.cc
index 87ae27f257e71819e8db89a87f66b70b16191302..49c17a19ea686892a49d41ee3631f0b21145885f 100644
--- a/content/browser/accessibility/browser_accessibility_win.cc
+++ b/content/browser/accessibility/browser_accessibility_win.cc
@@ -5418,9 +5418,12 @@ void BrowserAccessibilityWin::InitRoleAndState() {
         ia_role = ROLE_SYSTEM_PANE;
       }
       break;
-    case ui::AX_ROLE_ROW:
-      ia_role = ROLE_SYSTEM_ROW;
+    case ui::AX_ROLE_ROW: {
+      // Role changes depending on whether row is inside a treegrid
+      // https://www.w3.org/TR/core-aam-1.1/#role-map-row
+      ia_role = IsInTreeGrid(this) ? ROLE_SYSTEM_OUTLINEITEM : ROLE_SYSTEM_ROW;
       break;
+    }
     case ui::AX_ROLE_ROW_HEADER:
       ia_role = ROLE_SYSTEM_ROWHEADER;
       break;
@@ -5596,6 +5599,23 @@ void BrowserAccessibilityWin::InitRoleAndState() {
   win_attributes_->ia2_state = ia2_state;
 }
 
+bool BrowserAccessibilityWin::IsInTreeGrid(const BrowserAccessibility* item) {
+  BrowserAccessibility* container = item->PlatformGetParent();
+  if (container && container->GetRole() == ui::AX_ROLE_GROUP) {
+    // If parent was a rowgroup, we need to look at the grandparent
+    container = container->PlatformGetParent();
+  }
+
+  if (!container) {
+    return false;
+  }
+
+  const ui::AXRole role = container->GetRole();
+  return role == ui::AX_ROLE_TREE_GRID ||
+         (role == ui::AX_ROLE_TABLE &&
+          container->GetString16Attribute(ui::AX_ATTR_ROLE) == L"treegrid");
+}
+
 BrowserAccessibilityWin* ToBrowserAccessibilityWin(BrowserAccessibility* obj) {
   DCHECK(!obj || obj->IsNative());
   return static_cast<BrowserAccessibilityWin*>(obj);