[Ozone-DRI] Convert HardwareDisplayController to use scanout buffers

ui/ozone/platform/dri/gbm_surface.h

Index: ui/ozone/platform/dri/gbm_surface.h
diff --git a/ui/ozone/platform/dri/gbm_surface.h b/ui/ozone/platform/dri/gbm_surface.h
index a8c078a5523d156aab76a71e4a2728e33e5c5fc2..914680b9246749c639f9a22d22ced7170293484e 100644
--- a/ui/ozone/platform/dri/gbm_surface.h
+++ b/ui/ozone/platform/dri/gbm_surface.h
@@ -28,6 +28,10 @@ class GbmSurface : public ScanoutSurface {
   GbmSurface(gbm_device* device, DriWrapper* dri, const gfx::Size& size);
   virtual ~GbmSurface();
 
+  scoped_refptr<GbmBufferBase> backbuffer() const {
+    return buffers_[front_buffer_ ^ 1];
+  }
+
   // ScanoutSurface:
   virtual bool Initialize() OVERRIDE;
   virtual uint32_t GetFramebufferId() const OVERRIDE;