Unknown WebAXRole from Blink should be mapped to a valid chromium AX role.

content/renderer/accessibility/blink_ax_enum_conversion.cc

 // Copyright (c) 2013 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.
 
 #include "content/renderer/accessibility/blink_ax_enum_conversion.h"
 
 #include "base/logging.h"
 
 namespace content {
 
@@ skipping 315 matching lines @@
       return ui::AX_ROLE_TOOLTIP;
     case blink::WebAXRoleValueIndicator:
       return ui::AX_ROLE_VALUE_INDICATOR;
     case blink::WebAXRoleWebArea:
       return ui::AX_ROLE_WEB_AREA;
     case blink::WebAXRoleWindow:
       return ui::AX_ROLE_WINDOW;
     default:
       // We can't add an assertion here, that prevents us
       // from adding new role enums in Blink.
-      return static_cast<ui::AXRole>(-1);
+      LOG(WARNING) << "Warning: Blink WebAXRole " << role
+                   << " not handled by Chromium yet.";
+      return ui::AX_ROLE_UNKNOWN;
   }
 }
 
 ui::AXEvent AXEventFromBlink(blink::WebAXEvent event) {
   switch (event) {
     case blink::WebAXEventActiveDescendantChanged:
       return ui::AX_EVENT_ACTIVEDESCENDANTCHANGED;
     case blink::WebAXEventAlert:
       return ui::AX_EVENT_ALERT;
     case blink::WebAXEventAriaAttributeChanged:
@@ skipping 57 matching lines @@
     case blink::WebAXTextDirectionBT:
       return ui::AX_TEXT_DIRECTION_BT;
     default:
       NOTREACHED();
   }
 
   return ui::AX_TEXT_DIRECTION_NONE;
 }
 
 }  // namespace content