Add/remove surface references via MojoCompositorFrameSink.

cc/ipc/mojo_compositor_frame_sink.mojom

Index: cc/ipc/mojo_compositor_frame_sink.mojom
diff --git a/cc/ipc/mojo_compositor_frame_sink.mojom b/cc/ipc/mojo_compositor_frame_sink.mojom
index cedd96615e4edc5190470ac314d472cb60c4fd94..1e9859ba61b0901451b2e5a3a65e239cff62ae39 100644
--- a/cc/ipc/mojo_compositor_frame_sink.mojom
+++ b/cc/ipc/mojo_compositor_frame_sink.mojom
@@ -8,6 +8,7 @@ import "cc/ipc/begin_frame_args.mojom";
 import "cc/ipc/compositor_frame.mojom";
 import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/local_frame_id.mojom";
+import "cc/ipc/surface_reference.mojom";
 import "cc/ipc/returned_resource.mojom";
 
 // A MojoCompositorFrameSink is an interface for receiving CompositorFrame
@@ -31,6 +32,12 @@ interface MojoCompositorFrameSink {
   SubmitCompositorFrame(cc.mojom.LocalFrameId local_frame_id,
                         cc.mojom.CompositorFrame frame);
 
+  // Adds surface references.
+  AddSurfaceReferences(array<SurfaceReference> references);
+
+  // Removes surface references.
+  RemoveSurfaceReferences(array<SurfaceReference> references);
+
   // TODO(fsamuel): ReadbackBitmap API would be useful here.
 };