reinstate black-screenshot debugging code

turned off by default.

Bug: 10809349
Change-Id: I3e6b8c7860e6b0e122b8f07de4020967cd1f005c
diff --git a/services/surfaceflinger/RenderEngine/RenderEngine.h b/services/surfaceflinger/RenderEngine/RenderEngine.h
index 5f331d4..3c7f9ab 100644
--- a/services/surfaceflinger/RenderEngine/RenderEngine.h
+++ b/services/surfaceflinger/RenderEngine/RenderEngine.h
@@ -70,6 +70,7 @@
     void disableScissor();
     void genTextures(size_t count, uint32_t* names);
     void deleteTextures(size_t count, uint32_t const* names);
+    void readPixels(size_t l, size_t b, size_t w, size_t h, uint32_t* pixels);
 
     class BindImageAsFramebuffer {
         RenderEngine& mEngine;
@@ -106,8 +107,6 @@
     virtual size_t getMaxTextureSize() const = 0;
     virtual size_t getMaxViewportDims() const = 0;
 
-
-
     EGLContext getEGLContext() const;
 };