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/libs/vr/libvrflinger/hardware_composer.h b/libs/vr/libvrflinger/hardware_composer.h
index 8698814..bfce10b 100644
--- a/libs/vr/libvrflinger/hardware_composer.h
+++ b/libs/vr/libvrflinger/hardware_composer.h
@@ -381,6 +381,7 @@
     hardware::Return<void> onVsyncPeriodTimingChanged(
         Hwc2::Display display,
         const Hwc2::VsyncPeriodChangeTimeline& updatedTimeline) override;
+    hardware::Return<void> onSeamlessPossible(Hwc2::Display display) override;
 
     bool GotFirstHotplug() { return got_first_hotplug_; }
     void SetVsyncService(const sp<VsyncService>& vsync_service);