Debug code for detecting all black pixels screenshots

Bug: 9120292
Change-Id: If60db32524db973bb1f905ba3cb415c2a1cd7e71
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 089c265..cbedda7 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -400,6 +400,9 @@
         String8& result) const;
     bool startDdmConnection();
     static void appendSfConfigString(String8& result);
+    void checkScreenshot(const sp<GraphicBuffer>& buf, void const* vaddr,
+            const sp<const DisplayDevice>& hw,
+            uint32_t minLayerZ, uint32_t maxLayerZ);
 
     /* ------------------------------------------------------------------------
      * Attributes