mus-ws: Plumb FrameSinkId to Children

ui/aura/mus/mus_context_factory.cc

Index: ui/aura/mus/mus_context_factory.cc
diff --git a/ui/aura/mus/mus_context_factory.cc b/ui/aura/mus/mus_context_factory.cc
index 6a099290099ae219480c4a97d669c738448d8cfd..be536b8821c34bae64e161853c9f7a629fc06daa 100644
--- a/ui/aura/mus/mus_context_factory.cc
+++ b/ui/aura/mus/mus_context_factory.cc
@@ -26,9 +26,18 @@ void MusContextFactory::OnEstablishedGpuChannel(
       WindowTreeHost::GetForAcceleratedWidget(compositor->widget());
   WindowPortMus* window_port = WindowPortMus::Get(host->window());
   DCHECK(window_port);
-  auto compositor_frame_sink = window_port->RequestCompositorFrameSink(
+  window_port->RequestCompositorFrameSink(
       gpu_->CreateContextProvider(std::move(gpu_channel)),
-      gpu_->gpu_memory_buffer_manager());
+      gpu_->gpu_memory_buffer_manager(),
+      base::Bind(&MusContextFactory::OnCompositorFrameSinkAvailable,
+                 weak_ptr_factory_.GetWeakPtr(), compositor));
+}
+
+void MusContextFactory::OnCompositorFrameSinkAvailable(
+    base::WeakPtr<ui::Compositor> compositor,
+    std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink) {
+  if (!compositor)
+    return;
   compositor->SetCompositorFrameSink(std::move(compositor_frame_sink));
 }