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

ui/gl/gl_surface_ozone.cc

Index: ui/gl/gl_surface_ozone.cc
diff --git a/ui/gl/gl_surface_ozone.cc b/ui/gl/gl_surface_ozone.cc
index 67ab131b7a8c261905ca7fe5bc0a5aef855e2adb..db588c2135dbaefcb64a175566ab766cde0914b2 100644
--- a/ui/gl/gl_surface_ozone.cc
+++ b/ui/gl/gl_surface_ozone.cc
@@ -144,6 +144,18 @@ class GL_EXPORT GLSurfaceOzoneSurfaceless : public SurfacelessEGL {
     SwapBuffers();
     return true;
   }
+  bool SwapBuffersAsync(const SwapCompletionCallback& callback) override {
+    // TODO: this should be replaced by a fence when supported by the driver.
+    glFlush();
+    return ozone_surface_->OnSwapBuffersAsync(callback);
+  }
+  bool PostSubBufferAsync(int x,
+                          int y,
+                          int width,
+                          int height,
+                          const SwapCompletionCallback& callback) override {
+    return SwapBuffersAsync(callback);
+  }
 
  private:
   virtual ~GLSurfaceOzoneSurfaceless() {