Add/remove surface references via MojoCompositorFrameSink.

cc/ipc/display_compositor.mojom

Index: cc/ipc/display_compositor.mojom
diff --git a/cc/ipc/display_compositor.mojom b/cc/ipc/display_compositor.mojom
index d8fab7a6763bd5a70fb02084d7af69a7310269b0..79ee4c2d2b63e212d35ea9cb825623237e5978cb 100644
--- a/cc/ipc/display_compositor.mojom
+++ b/cc/ipc/display_compositor.mojom
@@ -29,15 +29,6 @@ interface DisplayCompositor {
       cc.mojom.MojoCompositorFrameSink& compositor_frame_sink,
       cc.mojom.MojoCompositorFrameSinkPrivate& compositor_frame_sink_private,
       cc.mojom.MojoCompositorFrameSinkClient compositor_frame_sink_client);
-
-  // TODO(fsamuel): This surface reference API is temporary. Surface references
-  // should be bundled with CompositorFrames.
-  AddRootSurfaceReference(cc.mojom.SurfaceId child_id);
-  AddSurfaceReference(cc.mojom.SurfaceId parent_id,
-                      cc.mojom.SurfaceId child_id);
-  RemoveRootSurfaceReference(cc.mojom.SurfaceId child_id);
-  RemoveSurfaceReference(cc.mojom.SurfaceId parent_id,
-                         cc.mojom.SurfaceId child_id);
 };
 
 // The DisplayCompositorClient interface is implemented by the Display
@@ -45,6 +36,10 @@ interface DisplayCompositor {
 // compositor. The display compositor host is either the browser process in
 // Chrome or the window server process.
 interface DisplayCompositorClient {
+  // Called by the display compositor upon connection. Provides the top level
+  // root surface id that should reference display roots.
+  OnRootSurfaceId(cc.mojom.SurfaceId surface_id);

[Fady Samuel, 2016/12/04 23:30:12]

OnDisplayCompositorCreated?

"OnRootSurfaceId" doesn't tell me what just happened. We should always have a
root surface ID available when we need it, right? Could you please add a comment
explaining why that's the case?

[kylechar, 2016/12/05 20:26:44]

Done.

+
   // Called by the display compositor immediately upon receiving a
   // CompositorFrame with a new SurfaceId for the first time.
   OnSurfaceCreated(cc.mojom.SurfaceId surface_id,