ozone: dri: add synchronous SwapBuffers support on surfaceless

ui/ozone/platform/dri/gbm_surfaceless.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_surfaceless.h"
 
 #include "ui/ozone/platform/dri/dri_vsync_provider.h"
 #include "ui/ozone/platform/dri/dri_window_delegate.h"
 #include "ui/ozone/platform/dri/gbm_buffer.h"
 #include "ui/ozone/platform/dri/hardware_display_controller.h"
 
 namespace ui {
 
 GbmSurfaceless::GbmSurfaceless(DriWindowDelegate* window_delegate)
     : window_delegate_(window_delegate) {
 }
 
 GbmSurfaceless::~GbmSurfaceless() {}
 
 intptr_t GbmSurfaceless::GetNativeWindow() {
   NOTREACHED();
   return 0;
 }
 
 bool GbmSurfaceless::ResizeNativeWindow(const gfx::Size& viewport_size) {
   return true;
 }
 
 bool GbmSurfaceless::OnSwapBuffers() {
-  NOTREACHED();
-  return false;
+  HardwareDisplayController* controller = window_delegate_->GetController();
+  if (!controller)
+    return true;
+
+  return controller->PageFlip();
 }
 
 bool GbmSurfaceless::OnSwapBuffersAsync(
     const SwapCompletionCallback& callback) {
   HardwareDisplayController* controller = window_delegate_->GetController();
   if (!controller) {
     callback.Run();
     return true;
   }
 
   return controller->SchedulePageFlip(callback);
 }
 
 scoped_ptr<gfx::VSyncProvider> GbmSurfaceless::CreateVSyncProvider() {
   return make_scoped_ptr(new DriVSyncProvider(window_delegate_));
 }
 
 }  // namespace ui