Views a11y: Use AX_ROLE_POP_UP_BUTTON for views::Combobox.

ui/views/controls/combobox/combobox.cc

 // 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.
 
 #include "ui/views/controls/combobox/combobox.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 733 matching lines @@
 
   if (selector_)
     selector_->OnViewBlur();
   // Border renders differently when focused.
   SchedulePaint();
   if (UseMd())
     FocusRing::Uninstall(this);
 }
 
 void Combobox::GetAccessibleNodeData(ui::AXNodeData* node_data) {
-  node_data->role = ui::AX_ROLE_COMBO_BOX;
+  // AX_ROLE_COMBO_BOX is for UI elements with a dropdown and an editable text
+  // field, which views::Combobox does not have. Use AX_ROLE_POP_UP_BUTTON to
+  // match an HTML <select> element.
+  node_data->role = ui::AX_ROLE_POP_UP_BUTTON;
+
   node_data->SetName(accessible_name_);
   node_data->SetValue(model_->GetItemAt(selected_index_));
   if (enabled()) {
     node_data->AddIntAttribute(ui::AX_ATTR_DEFAULT_ACTION_VERB,
                                ui::AX_DEFAULT_ACTION_VERB_OPEN);
   }
   node_data->AddIntAttribute(ui::AX_ATTR_POS_IN_SET, selected_index_);
   node_data->AddIntAttribute(ui::AX_ATTR_SET_SIZE, model_->GetItemCount());
 }
 
@@ skipping 245 matching lines @@
   constexpr int kMdPaddingWidth = 8;
   constexpr int kNormalPaddingWidth = 7;
   int arrow_pad = UseMd() ? kMdPaddingWidth : kNormalPaddingWidth;
   int padding = style_ == STYLE_NORMAL
                     ? arrow_pad * 2
                     : kActionLeftPadding + kActionRightPadding;
   return ArrowSize().width() + padding;
 }
 
 }  // namespace views