WIP: Propagate SurfaceID up window tree hierarchy

services/ui/public/interfaces/surface.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module ui.mojom;
 
 import "cc/ipc/compositor_frame.mojom";
 import "cc/ipc/returned_resource.mojom";
 
 // A Surface is an interface for receiving CompositorFrame structs. This is a
 // separate interface to allow CompositorFrames to be delivered from
 // supplementary (not main) threads of a mojo app.
 interface Surface {
   // After the submitted frame is drawn for the first time, the receiver will
   // respond to the SubmitFrame message. Clients should use this acknowledgement
   // to ratelimit frame submissions.
+  // TODO(fsamuel): Add local ID and nonce.
   SubmitCompositorFrame(cc.mojom.CompositorFrame frame) => ();
 };
 
 interface SurfaceClient {
   ReturnResources(array<cc.mojom.ReturnedResource> resources);
 };