[Ozone-DRI] Re-enable GBM surface mode support

ui/ozone/platform/dri/gbm_surface.cc

 // 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.
 
 #include "ui/ozone/platform/dri/gbm_surface.h"
 
 #include <gbm.h>
 
 #include "base/bind.h"
 #include "base/logging.h"
@@ skipping 114 matching lines @@
 }
 
 bool GbmSurface::ResizeNativeWindow(const gfx::Size& viewport_size) {
   if (size_ == viewport_size)
     return true;
 
   return false;
 }
 
 bool GbmSurface::OnSwapBuffers() {
-  NOTREACHED();
-  return false;
+  return OnSwapBuffersAsync(base::Bind(&base::DoNothing));
 }
 
 bool GbmSurface::OnSwapBuffersAsync(const SwapCompletionCallback& callback) {
   DCHECK(native_surface_);
 
   gbm_bo* pending_buffer = gbm_surface_lock_front_buffer(native_surface_);
   scoped_refptr<GbmSurfaceBuffer> primary =
       GbmSurfaceBuffer::GetBuffer(pending_buffer);
   if (!primary.get()) {
     primary = GbmSurfaceBuffer::CreateBuffer(dri_, pending_buffer);
@@ skipping 22 matching lines @@
                                        gbm_bo* pending_buffer) {
   // If there was a frontbuffer, it is no longer active. Release it back to GBM.
   if (current_buffer_)
     gbm_surface_release_buffer(native_surface_, current_buffer_);
 
   current_buffer_ = pending_buffer;
   callback.Run();
 }
 
 }  // namespace ui