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

content/browser/renderer_host/popup_menu_helper_mac.mm

 // 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.
 
 #import <Carbon/Carbon.h>
 
 #include "content/browser/renderer_host/popup_menu_helper_mac.h"
 
 #import "base/mac/scoped_sending_event.h"
 #include "base/memory/scoped_nsobject.h"
@@ skipping 15 matching lines @@
       this, content::NOTIFICATION_RENDER_WIDGET_HOST_DESTROYED,
       content::Source<RenderWidgetHost>(render_view_host));
 }
 
 void PopupMenuHelper::ShowPopupMenu(
     const gfx::Rect& bounds,
     int item_height,
     double item_font_size,
     int selected_item,
     const std::vector<WebMenuItem>& items,
-    bool right_aligned) {
+    bool right_aligned,
+    bool allow_multiple_selection) {
+  // Only single selection list boxes show a popup on Mac.
+  DCHECK(!allow_multiple_selection);
+
   // Retain the Cocoa view for the duration of the pop-up so that it can't be
   // dealloced if my Destroy() method is called while the pop-up's up (which
   // would in turn delete me, causing a crash once the -runMenuInView
   // call returns. That's what was happening in <http://crbug.com/33250>).
   RenderWidgetHostViewMac* rwhvm =
       static_cast<RenderWidgetHostViewMac*>(render_view_host_->GetView());
   scoped_nsobject<RenderWidgetHostViewCocoa> cocoa_view
       ([rwhvm->cocoa_view() retain]);
 
   // Display the menu.
@@ skipping 35 matching lines @@
 
 void PopupMenuHelper::Observe(
     int type,
     const content::NotificationSource& source,
     const content::NotificationDetails& details) {
   DCHECK(type == content::NOTIFICATION_RENDER_WIDGET_HOST_DESTROYED);
   DCHECK(content::Source<RenderWidgetHost>(source).ptr() == render_view_host_);
   render_view_host_ = NULL;
 }