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

ui/ozone/platform/dri/gbm_surface.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_OZONE_PLATFORM_DRI_GBM_SURFACE_H_
 #define UI_OZONE_PLATFORM_DRI_GBM_SURFACE_H_
 
 #include "base/macros.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/ozone/platform/dri/gbm_surfaceless.h"
@@ skipping 19 matching lines @@
              gbm_device* device,
              DriWrapper* dri);
   ~GbmSurface() override;
 
   bool Initialize();
 
   // GbmSurfaceless:
   intptr_t GetNativeWindow() override;
   bool ResizeNativeWindow(const gfx::Size& viewport_size) override;
   bool OnSwapBuffers() override;
+  bool OnSwapBuffersAsync(const SwapCompletionCallback& callback) override;
 
  private:
   gbm_device* gbm_device_;
 
   DriWrapper* dri_;
 
   // The native GBM surface. In EGL this represents the EGLNativeWindowType.
   gbm_surface* native_surface_;
 
   // Buffer currently used for scanout.
   gbm_bo* current_buffer_;
 
   gfx::Size size_;
 
   DISALLOW_COPY_AND_ASSIGN(GbmSurface);
 };
 
 }  // namespace ui
 
 #endif  // UI_OZONE_PLATFORM_DRI_GBM_SURFACE_H_