WIP: Propagate SurfaceID up window tree hierarchy

cc/ipc/surface_id.mojom

 // Copyright 2014 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 cc.mojom;
 
+import "cc/ipc/frame_sink_id.mojom";
+
 // A surface ID is composed of three parts: a client ID, a local ID, and a
 // nonce. The local part and nonce are allocated by the client using any scheme
 // that avoids duplicates and makes IDs unguessable respectively. The client ID
 // is allocated by the service and will be different for each client.
 //
 // The special client_id value 0 is equivalent to the current client.
 // This can be used to create, destroy and submit frames to surfaces before
 // learning the client ID and to reference other surfaces owned by the same
 // client. The actual client ID must be used to pass surface ids to other
 // clients for them to reference.
 struct SurfaceId {
-  // A service allocated ID identifying a client.
-  uint32 client_id;
+  FrameSinkId frame_sink_id;
 
   // An identifier allocated by the client uniquely identifying a surface within
   // a client process.
   uint32 local_id;
 
   // A cryptographically secure random int chosen to make the SurfaceId
   // unguessable by other clients.
   uint64 nonce;
 };