compositor: Add a MetaSizeChange value for tiling.

The change type is passed to the plugin size-change signal, so
Cinnamon can tell what sort of size change is happening (max/unmax/
tile).

We expand on tiling enough that it merits its own change type.

Author: mtwebster

src/core/window.c

@@ -3430,7 +3430,7 @@ meta_window_tile (MetaWindow   *window,
   meta_window_get_buffer_rect (window, &old_buffer_rect);
 
   meta_compositor_size_change_window (window->display->compositor, window,
-                                      META_SIZE_CHANGE_MAXIMIZE,
+                                      META_SIZE_CHANGE_TILE,
                                       &old_frame_rect, &old_buffer_rect);
 
   meta_window_move_resize_internal (window,

src/meta/compositor.h

@@ -64,6 +64,7 @@ typedef enum
   META_SIZE_CHANGE_UNMAXIMIZE,
   META_SIZE_CHANGE_FULLSCREEN,
   META_SIZE_CHANGE_UNFULLSCREEN,
+  META_SIZE_CHANGE_TILE
 } MetaSizeChange;
 
 META_EXPORT