We want to make sure that the submenu action is changed back to FALSE
_after_ the menu item has been activated. This prevents the menu
teardown handler from deleting the menu item before it can be activated.
Unfortunately, GtkMenuShell emits "hide" before the item activation.
This is probably done to prevent the application from doing things like
showing dialogs when the menu is still holding the grab.
In the case where we are doing an activate, set a boolean flag on each
of the open menus (following the parent stack) indicating that we'll be
emitting another signal soon (selection done). If that flag is set, we
defer the setting of the submenu action until we receive the second
signal.
https://bugzilla.gnome.org/show_bug.cgi?id=729820
GtkMenuTracker folds a nested structure of sections in a GMenuModel into
a single linear menu, which it expresses to its user by means of 'insert
item at position' and 'remove item at position' callbacks.
The logic for where to insert separators and how to handle action
namespaces is contained within the tracker, removing the need to have
this logic duplicated in the 3 or 4 places that consume GMenuModel.
In comparison with the previous code, the tracker no longer completely
destroys and rebuilds menus every time a single change occurs. As a
result, the new gtkmenu testcase now runs in approximately 3 seconds
instead of ~60 before.
https://bugzilla.gnome.org/show_bug.cgi?id=696468
