Cache buffers if only source crop is moved and no other changes.

 - also add trunk flag to guard it

Bug: 305718400
Test: libcompositionengine_test
Change-Id: I071d3c3610ba8516529621a0b9f56298f0439e0c
diff --git a/services/surfaceflinger/common/FlagManager.cpp b/services/surfaceflinger/common/FlagManager.cpp
index 35dd428..a582232 100644
--- a/services/surfaceflinger/common/FlagManager.cpp
+++ b/services/surfaceflinger/common/FlagManager.cpp
@@ -122,6 +122,7 @@
     DUMP_READ_ONLY_FLAG(multithreaded_present);
     DUMP_READ_ONLY_FLAG(add_sf_skipped_frames_to_trace);
     DUMP_READ_ONLY_FLAG(use_known_refresh_rate_for_fps_consistency);
+    DUMP_READ_ONLY_FLAG(cache_if_source_crop_layer_only_moved);
 
 #undef DUMP_READ_ONLY_FLAG
 #undef DUMP_SERVER_FLAG
@@ -192,6 +193,8 @@
 FLAG_MANAGER_READ_ONLY_FLAG(multithreaded_present, "debug.sf.multithreaded_present")
 FLAG_MANAGER_READ_ONLY_FLAG(add_sf_skipped_frames_to_trace, "")
 FLAG_MANAGER_READ_ONLY_FLAG(use_known_refresh_rate_for_fps_consistency, "")
+FLAG_MANAGER_READ_ONLY_FLAG(cache_if_source_crop_layer_only_moved,
+                            "debug.sf.cache_source_crop_only_moved")
 
 /// Trunk stable server flags ///
 FLAG_MANAGER_SERVER_FLAG(late_boot_misc2, "")