SF: add a sysprop to control layer caching

Bug: 158790260
Test: SF unit tests
Change-Id: I7ce6e781a480ceeeefa515cdb20bb82b618f2291
diff --git a/services/surfaceflinger/SurfaceFlingerProperties.h b/services/surfaceflinger/SurfaceFlingerProperties.h
index 816cb09..b19d216 100644
--- a/services/surfaceflinger/SurfaceFlingerProperties.h
+++ b/services/surfaceflinger/SurfaceFlingerProperties.h
@@ -100,6 +100,8 @@
 
 bool enable_frame_rate_override(bool defaultValue);
 
+bool enable_layer_caching(bool defaultValue);
+
 } // namespace sysprop
 } // namespace android
 #endif // SURFACEFLINGERPROPERTIES_H_