Move stats push off of critical path

Collected a field trace where pushing the atom cost ~500 microseconds,
which is too long.

Bug: 158601958
Test: builds
Change-Id: Id2c67f6fd6a12bb62d4e7b5da382cec78f3ac1c6
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 4cfbddd..7744365 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -1281,6 +1281,8 @@
     // janky frames there are.
     nsecs_t mMissedFrameJankStart = 0;
     int32_t mMissedFrameJankCount = 0;
+    // Positive if jank should be uploaded in postComposition
+    nsecs_t mLastJankDuration = -1;
 
     int mFrameRateFlexibilityTokenCount = 0;