tooltips: hide tooltips before showing popups

because if there's a tooltip visible then popups fail to show
with the following warning:
"Gdk-WARNING **: Tried to map a popup with a non-top most parent"

This bug affect popups of the form:
 1) popups from gtk_menu_popup_{at_widget|at_rect|for_device}()

    This can be reproduce with a normal GtkComboBox that has a
    tooltip attached (eg. via GtkBuilder 'tooltip_text' attribute).
    Also see GtkLabel reproducer from gtk3-demo mentioned in #1785

 2) custom popups created with gtk_window_new (GTK_WINDOW_POPUP)

    A reproducer that shows this case is a GtkComboBox with
    the property 'appears-as-list'[1] set to TRUE (default is FALSE).

Fixes issue #1785

[1] https://developer.gnome.org/gtk3/stable/GtkComboBox.html#GtkComboBox--s-appears-as-list

gtk/gtkcombobox.c

@@ -44,6 +44,7 @@
 #include "gtkwindow.h"
 #include "gtktypebuiltins.h"
 #include "gtkprivate.h"
+#include "gtktooltipprivate.h"
 #include "gtkcomboboxprivate.h"
 
 #include <gobject/gvaluecollector.h>
@@ -2315,6 +2316,7 @@ gtk_combo_box_popup_for_device (GtkComboBox *combo_box,
       return;
     }
 
+  _gtk_tooltip_hide (GTK_WIDGET (combo_box));
   toplevel = gtk_widget_get_toplevel (GTK_WIDGET (combo_box));
   if (GTK_IS_WINDOW (toplevel))
     {

gtk/gtkmenu.c

@@ -133,6 +133,7 @@
 #include "gtkcssnodeprivate.h"
 #include "gtkstylecontextprivate.h"
 #include "gtkcssstylepropertyprivate.h"
+#include "gtktooltipprivate.h"
 
 #include "deprecated/gtktearoffmenuitem.h"
 
@@ -1824,6 +1825,7 @@ gtk_menu_popup_internal (GtkMenu             *menu,
   g_return_if_fail (GTK_IS_MENU (menu));
   g_return_if_fail (device == NULL || GDK_IS_DEVICE (device));
 
+  _gtk_tooltip_hide_in_display (gtk_widget_get_display (GTK_WIDGET (menu)));
   display = gtk_widget_get_display (GTK_WIDGET (menu));
 
   if (device == NULL)

gtk/gtktooltip.c

@@ -1280,6 +1280,22 @@ _gtk_tooltip_hide (GtkWidget *widget)
     gtk_tooltip_hide_tooltip (tooltip);
 }
 
+void
+_gtk_tooltip_hide_in_display (GdkDisplay *display)
+{
+  GtkTooltip *tooltip;
+
+  if (!display)
+    return;
+
+  tooltip = g_object_get_qdata (G_OBJECT (display), quark_current_tooltip);
+
+  if (!tooltip || !GTK_TOOLTIP_VISIBLE (tooltip))
+    return;
+
+  gtk_tooltip_hide_tooltip (tooltip);
+}
+
 static gboolean
 tooltips_enabled (GdkEvent *event)
 {

gtk/gtktooltipprivate.h

@@ -36,6 +36,7 @@ void _gtk_tooltip_focus_out              (GtkWidget          *widget);
 void _gtk_tooltip_toggle_keyboard_mode   (GtkWidget          *widget);
 void _gtk_tooltip_handle_event           (GdkEvent           *event);
 void _gtk_tooltip_hide                   (GtkWidget          *widget);
+void _gtk_tooltip_hide_in_display        (GdkDisplay         *display);
 
 GtkWidget * _gtk_widget_find_at_coords   (GdkWindow          *window,
                                           gint                window_x,