Add trunk flag for adding SF skipped frames into traces.

Bug: 273701290
Test: FrameTimelineTest#traceDisplayFrameSkipped, play with perfetto
Change-Id: Ib5f884a14dc6526e2a2b5a1371be7715a20cd0a9
diff --git a/services/surfaceflinger/surfaceflinger_flags.aconfig b/services/surfaceflinger/surfaceflinger_flags.aconfig
index bb3c94a..71c59b2 100644
--- a/services/surfaceflinger/surfaceflinger_flags.aconfig
+++ b/services/surfaceflinger/surfaceflinger_flags.aconfig
@@ -71,6 +71,14 @@
 }
 
 flag {
+  name: "add_sf_skipped_frames_to_trace"
+  namespace: "core_graphics"
+  description: "Add SurfaceFlinger dropped Frames to frame timeline"
+  bug: "273701290"
+  is_fixed_read_only: true
+}
+
+flag {
   name: "refresh_rate_overlay_on_external_display"
   namespace: "core_graphics"
   description: "enable refresh rate indicator on the external display"