Add NativePixmapHandle type & interface for exporting them

ui/ozone/public/native_pixmap.h

Index: ui/ozone/public/native_pixmap.h
diff --git a/ui/ozone/public/native_pixmap.h b/ui/ozone/public/native_pixmap.h
index 0251a12246d41a0cf91e553bedb316d93bf296a8..c49530a367ca02827b1669271e6da42c68798bf6 100644
--- a/ui/ozone/public/native_pixmap.h
+++ b/ui/ozone/public/native_pixmap.h
@@ -7,10 +7,13 @@
 
 #include "base/bind.h"
 #include "base/memory/ref_counted.h"
+#include "ui/gfx/buffer_types.h"
+#include "ui/gfx/native_pixmap_handle_ozone.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/overlay_transform.h"
 
 namespace gfx {
+class NativePixmapHandle;
 class Rect;
 class RectF;
 }
@@ -53,6 +56,10 @@ class NativePixmap : public base::RefCountedThreadSafe<NativePixmap> {
   virtual void SetScalingCallback(const ScalingCallback& scaling_callback) = 0;
   virtual scoped_refptr<NativePixmap> GetScaledPixmap(gfx::Size new_size) = 0;
 
+  // Export the buffer for sharing across processes.
+  // Any file descriptors in the exported handle are owned by the caller.
+  virtual gfx::NativePixmapHandle ExportHandle() = 0;
+
  protected:
   virtual ~NativePixmap() {}