Move ReferencedSurfaceTracker into GpuCompositorFrameSink.

services/ui/ws/window_server.cc

Index: services/ui/ws/window_server.cc
diff --git a/services/ui/ws/window_server.cc b/services/ui/ws/window_server.cc
index aaafe893b449a7217c0ad9c67bfd5d9b57c20a66..0bf97ea295c503d7a332a5bc7456b6538e530a13 100644
--- a/services/ui/ws/window_server.cc
+++ b/services/ui/ws/window_server.cc
@@ -532,11 +532,6 @@ cc::mojom::DisplayCompositor* WindowServer::GetDisplayCompositor() {
   return display_compositor_.get();
 }
 
-const cc::SurfaceId& WindowServer::GetRootSurfaceId() const {
-  DCHECK(root_surface_id_.local_frame_id().is_valid());
-  return root_surface_id_;
-}
-
 bool WindowServer::GetFrameDecorationsForUser(
     const UserId& user_id,
     mojom::FrameDecorationValuesPtr* values) {
@@ -806,11 +801,6 @@ void WindowServer::OnSurfaceCreated(const cc::SurfaceInfo& surface_info) {
     window_tree->ProcessWindowSurfaceChanged(window, surface_info);
 }
 
-void WindowServer::OnDisplayCompositorCreated(
-    const cc::SurfaceId& root_surface_id) {
-  root_surface_id_ = root_surface_id;
-}
-
 void WindowServer::OnActiveUserIdChanged(const UserId& previously_active_id,
                                          const UserId& active_id) {
 }