[Ozone-DRI] Convert HardwareDisplayController to use scanout buffers

ui/ozone/platform/dri/dri_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/dri_surface.h"
 
 #include <errno.h>
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <xf86drm.h>
@@ skipping 42 matching lines @@
   CHECK(backbuffer());
   return backbuffer()->GetHandle();
 }
 
 void DriSurface::PreSwapBuffers() {
 }
 
 // This call is made after the hardware just started displaying our back buffer.
 // We need to update our pointer reference and synchronize the two buffers.
 void DriSurface::SwapBuffers() {
-  CHECK(frontbuffer());
   CHECK(backbuffer());
 
   // Update our front buffer pointer.
   front_buffer_ ^= 1;
 }
 
 gfx::Size DriSurface::Size() const {
   return size_;
 }
 
 SkCanvas* DriSurface::GetDrawableForWidget() {
   CHECK(backbuffer());
   return backbuffer()->GetCanvas();
 }
 
 }  // namespace ui