Boost priority of short-running SF FIFO threads slightly.

The short-running FIFO threads should preempt the SurfaceFlinger main
thread in order to prevent deadlock.

bug 31223682

Change-Id: I29e7b4b8439bb876998a8aeeb2b8d6ee5b6b7d36
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 2a67f4c..92c6571 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -471,7 +471,7 @@
 
         // set SFEventThread to SCHED_FIFO to minimize jitter
         struct sched_param param = {0};
-        param.sched_priority = 1;
+        param.sched_priority = 2;
         if (sched_setscheduler(mSFEventThread->getTid(), SCHED_FIFO, &param) != 0) {
             ALOGE("Couldn't set SCHED_FIFO for SFEventThread");
         }