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..cbfe1717dda3393bb0a29bf7ee6d1d0123b14c24 100644
--- a/ui/ozone/platform/drm/gpu/gbm_buffer.cc
+++ b/ui/ozone/platform/drm/gpu/gbm_buffer.cc
@@ -94,6 +94,18 @@ scoped_refptr<NativePixmap> GbmPixmap::GetScaledPixmap(gfx::Size new_size) {
   return scaling_callback_.Run(new_size);
 }
 
+bool GbmPixmap::ExportHandle(gfx::NativePixmapHandle* handle) {
+  int dmabuf_fd = dup(dma_buf_);
+  if (dmabuf_fd < 0) {
+    PLOG(ERROR) << "dup";
+    return false;
+  }
+
+  handle->fd = base::FileDescriptor(base::ScopedFD(dmabuf_fd));
+  handle->stride = gbm_bo_get_stride(buffer_->bo());
+  return true;
+}
+
 GbmPixmap::~GbmPixmap() {
   if (dma_buf_ > 0)
     close(dma_buf_);