Shell wants way to associate initially requested window creation state with the window later created

[Gerry Boland]

Use-case is for a multi-mode shell, where window management policy differs in each mode. Mode 1 is tablet mode, where shell must override the surface size requested by the client. Mode 2 is desktop where the surface size requested by the client is honoured.

Desired behaviour:
User launches app in tablet mode. Window of size a1,b1 requested, shell overrides and returns a2,b2. User switches to desktop mode, shell resizes window to a1,b1.

Problem:
Shell implements the tablet override with WMP::place_new_surface which is passed a WindowSpecification
When Mir creates the surface, it then calls WMP::advise_new_window. But shell has no identifier to associate the about-to-be-created window in WMP::place_new_surface with the created window in WMP::advise_new_window

If it has this identifier, it could remember the initially requested window state itself and apply that on mode change.

[Alan Griffiths (alan-griffiths)]

if we added a user_data property onto the WindowSpecification and miral copied that to the WindowInfo it would help