Fix loss of mouse events when an Aura combobox is open in a modal dialog.

NativeComboboxViews was not passing itself as a (transient) parent to
MenuRunner::RunMenuAt. All mouse events were sent to the open menu (since it
is set as the capture window), and ModalityEventFilter::PreHandleMouseEvent
dropped them all since they were not directed to a child of the active modal
dialog.


BUG=105155
TEST=none


Review URL: http://codereview.chromium.org/8893019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113978 0039d316-1c4b-4281-b951-d872f2087c98

ui/views/controls/combobox/native_combobox_views.cc

@@ -361,7 +361,7 @@ void NativeComboboxViews::ShowDropDownMenu() {
 
   dropdown_open_ = true;
   if (dropdown_list_menu_runner_->RunMenuAt(
-          NULL, NULL, bounds, MenuItemView::TOPLEFT,
+          GetWidget(), NULL, bounds, MenuItemView::TOPLEFT,
           MenuRunner::HAS_MNEMONICS) == MenuRunner::MENU_DELETED)
     return;
   dropdown_open_ = false;