Add NativePixmapHandle type & interface for exporting them

ui/ozone/platform/drm/gpu/gbm_buffer.cc

Index: ui/ozone/platform/drm/gpu/gbm_buffer.cc
diff --git a/ui/ozone/platform/drm/gpu/gbm_buffer.cc b/ui/ozone/platform/drm/gpu/gbm_buffer.cc
index b47dc5438e472e30714fbe7f4cd1d8e076a8c8cd..7135f2fdcf7e7a8c2ab798d812d90739d62178d0 100644
--- a/ui/ozone/platform/drm/gpu/gbm_buffer.cc
+++ b/ui/ozone/platform/drm/gpu/gbm_buffer.cc
@@ -10,8 +10,10 @@
 #include <xf86drm.h>
 
 #include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/gfx/geometry/size_conversions.h"
+#include "ui/gfx/native_pixmap_handle_ozone.h"
 #include "ui/ozone/platform/drm/gpu/drm_window.h"
 #include "ui/ozone/platform/drm/gpu/gbm_device.h"
 
@@ -94,6 +96,20 @@ scoped_refptr<NativePixmap> GbmPixmap::GetScaledPixmap(gfx::Size new_size) {
   return scaling_callback_.Run(new_size);
 }
 
+gfx::NativePixmapHandle GbmPixmap::ExportHandle() {
+  gfx::NativePixmapHandle handle;
+
+  int dmabuf_fd = HANDLE_EINTR(dup(dma_buf_));
+  if (dmabuf_fd < 0) {
+    PLOG(ERROR) << "dup";
+    return handle;
+  }
+
+  handle.fd = base::FileDescriptor(dmabuf_fd, true /* auto_close */);
+  handle.stride = gbm_bo_get_stride(buffer_->bo());
+  return handle;
+}
+
 GbmPixmap::~GbmPixmap() {
   if (dma_buf_ > 0)
     close(dma_buf_);