SurfaceFlinger: plumb composer 2.4 onSeamlessPossible

Plumb onSeamlessPossible callback to SurfaceFlinger.

Test: rev up composer to 2.4
Bug: 141329414
Change-Id: I2166b8ea066002c76781aacbcc985f85f7c255a8
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 2f84b13..dcd9dc2 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -505,6 +505,7 @@
     void onVsyncPeriodTimingChangedReceived(
             int32_t sequenceId, hwc2_display_t display,
             const hwc_vsync_period_change_timeline_t& updatedTimeline) override;
+    void onSeamlessPossible(int32_t sequenceId, hwc2_display_t display) override;
 
     /* ------------------------------------------------------------------------
      * ISchedulerCallback