Defer Gtk.Window.iconify

Defer iconify call to after the activity has been shown.  Remember the
iconify call was requested, and make the call just prior to entering the
main loop.

On Ubuntu 18.04 with Metacity 3.32.0 the Journal does appear over the
Home View on Sugar start on a VM with two virtual CPUs, yet the previous
fix in Metacity (074af8f) is present.  This is suggestive of a race
condition.

Tests with a minimal GTK reproducer shows order of three specific calls
is critical to success of iconify.  The ordering and results are;

* iconify, maximize, show; not iconified,

* maximize, iconify, show; not iconified,

* iconify, show, maximize; not iconified,

* maximize, show, iconify; app with focus will flicker, iconified,

* show, maximize, iconify; app with focus may flicker, iconified,

* show, iconify, maximize; app with focus may flicker, iconified,

Sugar Toolkit combined with Journal uses the "maximize, iconify, show"
ordering.  Using a Hello World activity with a call to iconify, the new
activity is not iconified.

When changed to "mazimise, show, iconify" ordering, there is no flicker
of the app in focus, and the new activity is iconified.

src/sugar3/activity/activity.py

@@ -361,6 +361,8 @@ class Activity(Window, Gtk.Container):
         self.connect('realize', self.__realize_cb)
         self.connect('delete-event', self.__delete_event_cb)
 
+        self._in_main = False
+        self._iconify = False
         self._active = False
         self._active_time = None
         self._spent_time = 0
@@ -468,7 +470,16 @@ class Activity(Window, Gtk.Container):
         """
         self._stop_buttons.append(button)
 
+    def iconify(self):
+        if not self._in_main:
+            self._iconify = True  # i.e. do after Window.show()
+        else:
+            Window.iconify(self)
+
     def run_main_loop(self):
+        if self._iconify:
+            Window.iconify(self)
+        self._in_main = True
         Gtk.main()
 
     def _initialize_journal_object(self):