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

ui/ozone/platform/egltest/ozone_platform_egltest.cc

Index: ui/ozone/platform/egltest/ozone_platform_egltest.cc
diff --git a/ui/ozone/platform/egltest/ozone_platform_egltest.cc b/ui/ozone/platform/egltest/ozone_platform_egltest.cc
index 4403635476023c0478c925a4d7166b2304f02110..8b2262548f4c16e285c09e843221ee0e3525ed24 100644
--- a/ui/ozone/platform/egltest/ozone_platform_egltest.cc
+++ b/ui/ozone/platform/egltest/ozone_platform_egltest.cc
@@ -209,6 +209,11 @@ class SurfaceOzoneEgltest : public SurfaceOzoneEGL {
 
   bool OnSwapBuffers() override { return true; }
 
+  bool OnSwapBuffersAsync(const SwapCompletionCallback& callback) override {
+    callback.Run();
+    return true;
+  }
+
   bool ResizeNativeWindow(const gfx::Size& viewport_size) override {
     return true;
   }