When clicking rapidly 2 different select popups, we could reach a state where

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index 841f41c6d1d1c1a6f5dbfbc66325f7ad63d443eb..4c10e5cd37ca6ca9b289c2b47aecdb092515ce86 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -1580,7 +1580,14 @@ WebWidget* RenderViewImpl::createPopupMenu(const WebPopupMenuInfo& info) {
 WebExternalPopupMenu* RenderViewImpl::createExternalPopupMenu(
     const WebPopupMenuInfo& popup_menu_info,
     WebExternalPopupMenuClient* popup_menu_client) {
-  DCHECK(!external_popup_menu_.get());
+  // An IPC message is sent to the browser to build and display the actual
+  // popup.  The user could have time to click a different select by the time
+  // the popup is shown.  In that case external_popup_menu_ is non NULL.
+  // By returning NULL in that case, we instruct WebKit to cancel that new
+  // popup.  So from the user perspective, only the first one will show, and
+  // will have to close the first one before another one can be shown.

[Ilya Sherman, 2012/05/14 23:26:04]

nit: Perhaps update this comment to mention that the |extenral_popup_menu_| can
also be non-NULL in case we haven't received the SelectPopupMenuItem message
yet?

+  if (external_popup_menu_.get())
+    return NULL;
   external_popup_menu_.reset(
       new ExternalPopupMenu(this, popup_menu_info, popup_menu_client));
   return external_popup_menu_.get();