drm_hwcomposer: fix buffer leak when using the GL compositor inside DrmDisplayCompositor

Change-Id: Id3a6deea9fc0f97640b34dacb25d36f3793f2d4e
diff --git a/drmdisplaycomposition.h b/drmdisplaycomposition.h
index 9c51078..7202c7c 100644
--- a/drmdisplaycomposition.h
+++ b/drmdisplaycomposition.h
@@ -67,6 +67,8 @@
   DrmCompositionLayerVector_t *GetCompositionLayers();
   uint32_t dpms_mode() const;
 
+  Importer *importer() const;
+
  private:
   DrmDisplayComposition(const DrmDisplayComposition &) = delete;