SF: VSyncPredictor correct calculation

Correct a miscalculation in vsync predictions that led to
a missed callback.

Bug: 144707443
Fixes: 145667109
Test: boot to home, scroll shade and news
Test: 1 new unit test that forces the error condition:

Change-Id: Idef8018326f965fab42a450e8a954cb93fcad905
diff --git a/services/surfaceflinger/Scheduler/Timer.cpp b/services/surfaceflinger/Scheduler/Timer.cpp
index 2394ed2..fb4f315 100644
--- a/services/surfaceflinger/Scheduler/Timer.cpp
+++ b/services/surfaceflinger/Scheduler/Timer.cpp
@@ -85,7 +85,7 @@
     };
 
     if (timerfd_settime(mTimerFd, 0, &new_timer, &old_timer)) {
-        ALOGW("Failed to set timerfd");
+        ALOGW("Failed to set timerfd %s (%i)", strerror(errno), errno);
     }
 }