Multi-select <select> in 'external popup window'

content/browser/web_contents/web_contents_view_gtk.cc

Index: content/browser/web_contents/web_contents_view_gtk.cc
diff --git a/content/browser/web_contents/web_contents_view_gtk.cc b/content/browser/web_contents/web_contents_view_gtk.cc
index d118130ca2764e517abaf7c1436ac4dd7411aaf5..4f2b0ce8ea14011449503672a7695871937e4ca7 100644
--- a/content/browser/web_contents/web_contents_view_gtk.cc
+++ b/content/browser/web_contents/web_contents_view_gtk.cc
@@ -332,6 +332,17 @@ void WebContentsViewGtk::ShowContextMenu(
     DLOG(ERROR) << "Cannot show context menus without a delegate.";
 }
 
+void WebContentsViewGtk::ShowPopupMenu(const gfx::Rect& bounds,
+                                       int item_height,
+                                       double item_font_size,
+                                       int selected_item,
+                                       const std::vector<WebMenuItem>& items,
+                                       bool right_aligned,
+                                       bool allow_multiple_selection) {
+  // External popup menus are only used on Mac and Android.
+  NOTIMPLEMENTED();
+}
+
 // Render view DnD -------------------------------------------------------------
 
 void WebContentsViewGtk::StartDragging(const WebDropData& drop_data,