WIP: Propagate SurfaceID up window tree hierarchy

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index de0b9c7cb0690fa0348ba6a2ee0424604c15c77f..8d95b27e910034e63b736565d60de7e5d017e72d 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -5,6 +5,7 @@
 module ui.mojom;
 
 import "cc/ipc/surface_id.mojom";
+import "cc/ipc/surface_sequence.mojom";
 import "services/ui/public/interfaces/cursor.mojom";
 import "services/ui/public/interfaces/event_matcher.mojom";
 import "services/ui/public/interfaces/mus_constants.mojom";
@@ -142,6 +143,10 @@ interface WindowTree {
                 Surface& surface,
                 SurfaceClient client);
 
+  // Returns reference to the surface.
+  SatisfySurfaceSequence(uint32 window_id,
+                         cc.mojom.SurfaceSequence sequence);
+
   // Reparents a window.
   // This fails for any of the following reasons:
   // . |parent| or |child| does not identify a valid window.
@@ -340,6 +345,13 @@ interface WindowTreeClient {
                         gfx.mojom.Rect old_bounds,
                         gfx.mojom.Rect new_bounds);
 
+  // Invoked when a client window submits a new surface ID.
+  OnWindowSurfaceCreated(uint32 window_id,
+                         gfx.mojom.Size size,
+                         float device_scale_factor,
+                         cc.mojom.SurfaceId surface_id,
+                         cc.mojom.SurfaceSequence surface_sequence);
+
   OnClientAreaChanged(uint32 window_id,
                       gfx.mojom.Insets new_client_area,
                       array<gfx.mojom.Rect> new_additional_client_areas);