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/DisplayHardware/HWC2.h b/services/surfaceflinger/DisplayHardware/HWC2.h
index 8b532e3..e7cf5ff 100644
--- a/services/surfaceflinger/DisplayHardware/HWC2.h
+++ b/services/surfaceflinger/DisplayHardware/HWC2.h
@@ -76,6 +76,7 @@
     virtual void onVsyncPeriodTimingChangedReceived(
             int32_t sequenceId, hwc2_display_t display,
             const hwc_vsync_period_change_timeline_t& updatedTimeline) = 0;
+    virtual void onSeamlessPossible(int32_t sequenceId, hwc2_display_t display) = 0;
 
     virtual ~ComposerCallback() = default;
 };