An unknown role is considered a bug, should never occur

third_party/WebKit/Source/modules/accessibility/AXNodeObject.cpp

 /*
  * Copyright (C) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 667 matching lines @@
 AccessibilityRole AXNodeObject::DetermineAccessibilityRole() {
   if (!GetNode())
     return kUnknownRole;
 
   if ((aria_role_ = DetermineAriaRoleAttribute()) != kUnknownRole)
     return aria_role_;
   if (GetNode()->IsTextNode())
     return kStaticTextRole;
 
   AccessibilityRole role = NativeAccessibilityRoleIgnoringAria();
-  if (role != kUnknownRole)
-    return role;
-  if (GetNode()->IsElementNode()) {
-    Element* element = ToElement(GetNode());
-    // A generic element with tabIndex explicitly set gets GroupRole.
-    // The layout checks for focusability aren't critical here; a false
-    // positive would be harmless.
-    if (element->IsInCanvasSubtree() && element->SupportsFocus())
-      return kGenericContainerRole;
-  }
-  return kUnknownRole;
+  return role == kUnknownRole ? kGenericContainerRole : role;
 }
 
 AccessibilityRole AXNodeObject::DetermineAriaRoleAttribute() const {
   const AtomicString& aria_role =
       GetAOMPropertyOrARIAAttribute(AOMStringProperty::kRole);
   if (aria_role.IsNull() || aria_role.IsEmpty())
     return kUnknownRole;
 
   AccessibilityRole role = AriaRoleToWebCoreRole(aria_role);
 
@@ skipping 2520 matching lines @@
     return String();
   return ToTextControlElement(node)->StrippedPlaceholder();
 }
 
 DEFINE_TRACE(AXNodeObject) {
   visitor->Trace(node_);
   AXObjectImpl::Trace(visitor);
 }
 
 }  // namespace blink