[ozone] Add stub async swap buffers implementation to ozone surfaceless.

ui/ozone/platform/dri/gbm_surface.cc

Index: ui/ozone/platform/dri/gbm_surface.cc
diff --git a/ui/ozone/platform/dri/gbm_surface.cc b/ui/ozone/platform/dri/gbm_surface.cc
index a4e624f768bdb10a0d29409dc7086dfe79cead6d..e4940a0a1558ba0a9da622bfdc91e1ac51c6446d 100644
--- a/ui/ozone/platform/dri/gbm_surface.cc
+++ b/ui/ozone/platform/dri/gbm_surface.cc
@@ -158,4 +158,10 @@ bool GbmSurface::OnSwapBuffers() {
   return true;
 }
 
+bool GbmSurface::OnSwapBuffersAsync(const SwapCompletionCallback& callback) {
+  bool success = OnSwapBuffers();
+  callback.Run();
+  return success;
+}
+
 }  // namespace ui