Allow the notification stack to be moved using DBus

lib/WindowManager.vala

@@ -165,6 +165,14 @@ namespace Gala {
          */
         public abstract void perform_action (ActionType type);
 
+        /**
+         * Tells the window manager to move the Notifications Stack down
+         * by the given number of pixels, to make room for menus.
+         *
+         * @param offset The amount of pixels by which to move the notifications stack
+         */
+        public abstract void offset_notifications (int32 offset);
+
         /**
          * Moves the window to the workspace next to its current workspace in the given direction.
          * Gala currently only supports LEFT and RIGHT.

src/DBus.vala

@@ -91,6 +91,10 @@ namespace Gala {
             wm.perform_action (type);
         }
 
+        public void offset_notifications (int32 offset) throws DBusError, Error {
+            wm.offset_notifications (offset);
+        }
+
         private const double SATURATION_WEIGHT = 1.5;
         private const double WEIGHT_THRESHOLD = 1.0;
 

src/NotificationStack.vala

@@ -22,7 +22,7 @@ public class Gala.NotificationStack : Object {
 
     // we need to keep a small offset to the top, because we clip the container to
     // its allocations and the close button would be off for the first notification
-    private const int TOP_OFFSET = 2;
+    private int TOP_OFFSET = 2;
     private const int ADDITIONAL_MARGIN = 12;
     private const int MARGIN = 12;
 
@@ -146,6 +146,11 @@ public class Gala.NotificationStack : Object {
         }
     }
 
+    public void offset_notifications (int32 offset) {
+        TOP_OFFSET = 2 + offset;
+        update_positions (true);
+    }
+
     public void destroy_notification (Meta.WindowActor notification, bool animate) {
         if (animate) {
             notification.save_easing_state ();

src/WindowManager.vala

@@ -901,6 +901,10 @@ namespace Gala {
             }
         }
 
+        public void offset_notifications (int32 offset) {
+            notification_stack.offset_notifications (offset);
+        }
+
         public override void show_window_menu (Meta.Window window, Meta.WindowMenuType menu, int x, int y) {
             switch (menu) {
                 case Meta.WindowMenuType.WM: