Update FrameInterval using next vsync generated

use the expectedPresentTime + threshold to get
the next frames interval.

Test: atrace and atest libsurfaceflinger_unittest --test-filter="SchedulerTest*"
BUG: 296636176
Change-Id: I9eb0d2784a81491028ec13d579356da2f34b85df
diff --git a/services/surfaceflinger/Scheduler/Scheduler.h b/services/surfaceflinger/Scheduler/Scheduler.h
index 0615b31..0f2364e 100644
--- a/services/surfaceflinger/Scheduler/Scheduler.h
+++ b/services/surfaceflinger/Scheduler/Scheduler.h
@@ -312,6 +312,9 @@
         return pacesetterSelectorPtr()->getActiveMode().fps;
     }
 
+    Fps getNextFrameInterval(PhysicalDisplayId, TimePoint currentExpectedPresentTime) const
+            EXCLUDES(mDisplayLock);
+
     // Returns the framerate of the layer with the given sequence ID
     float getLayerFramerate(nsecs_t now, int32_t id) const {
         return mLayerHistory.getLayerFramerate(now, id);