fix circular dependency libnativewindow <-> libui

Bug: 37647680
Bug: 37648355
Test: compile, manual
Change-Id: I9631beea52e23ebb519411f943c6f5062aedd2e5
diff --git a/libs/vr/libdvr/dvr_internal.h b/libs/vr/libdvr/dvr_internal.h
index 89bef09..6431f1c 100644
--- a/libs/vr/libdvr/dvr_internal.h
+++ b/libs/vr/libdvr/dvr_internal.h
@@ -44,6 +44,8 @@
 
 extern "C" {
 
+struct ANativeWindow;
+
 struct DvrWriteBuffer {
   std::shared_ptr<android::dvr::BufferProducer> write_buffer;
 };