SurfaceFlinger: Add "Abstract" Layer type.

Add an Abstract Layer type which exists only to be a parent. We
will use this to more cleanly represent the various hierarchy Layers
from the WM and for an upcoming screenshot rework.

Bug: 72760590
Test: Existing tests pass
Change-Id: Icd19ab0a467585660a95ae37b9c5dd4b8106da9d
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index ef8c7b0..ab004f2 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -17,7 +17,6 @@
 #ifndef ANDROID_LAYER_H
 #define ANDROID_LAYER_H
 
-#include <stdint.h>
 #include <sys/types.h>
 
 #include <utils/RefBase.h>
@@ -35,6 +34,7 @@
 #include <gui/BufferQueue.h>
 
 #include <list>
+#include <cstdint>
 
 #include "Client.h"
 #include "FrameTracker.h"