SF: omit vsync callbacks when screen is OFF

This CL is submitted behind a flag and in still in development.
The flag should not be enabled just yet.

Test: manual
Bug: 331636736
Flag: com.android.graphics.surfaceflinger.flags.no_vsyncs_on_screen_off
Change-Id: Iec9cde3bafb9c112c9ce9beebe6dded4727fc99c
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 31218ed..b9c4368 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -1423,6 +1423,11 @@
     // Whether a display should be turned on when initialized
     bool mSkipPowerOnForQuiescent;
 
+    // used for omitting vsync callbacks to apps when the display is not updatable
+    int mRefreshableDisplays GUARDED_BY(mStateLock) = 0;
+    void incRefreshableDisplays() REQUIRES(mStateLock);
+    void decRefreshableDisplays() REQUIRES(mStateLock);
+
     frontend::LayerLifecycleManager mLayerLifecycleManager GUARDED_BY(kMainThreadContext);
     frontend::LayerHierarchyBuilder mLayerHierarchyBuilder GUARDED_BY(kMainThreadContext);
     frontend::LayerSnapshotBuilder mLayerSnapshotBuilder GUARDED_BY(kMainThreadContext);