fix circular dependency libnativewindow <-> libui

Bug: 37647680, 37648355
Test: compile, manual
Change-Id: I00d72d063c252739ca5a63dbf84424ad4f837f89
diff --git a/libs/hwui/Readback.h b/libs/hwui/Readback.h
index b763953..7cf4262 100644
--- a/libs/hwui/Readback.h
+++ b/libs/hwui/Readback.h
@@ -20,10 +20,10 @@
 #include "Rect.h"
 
 #include <SkBitmap.h>
-#include <gui/Surface.h>
 
 namespace android {
 class GraphicBuffer;
+class Surface;
 namespace uirenderer {
 
 // Keep in sync with PixelCopy.java codes