SurfaceFlinger: give SF its own vsync phase

This change allows SurfaceFlinger to run at a different vsync phase offset from
that used by external listeners.

Bug: 11175503
Change-Id: I561c53a5659fa6dc1e3e4ae30340f3c1a6adceb4
diff --git a/services/surfaceflinger/Android.mk b/services/surfaceflinger/Android.mk
index 36ad741..c3daa64 100644
--- a/services/surfaceflinger/Android.mk
+++ b/services/surfaceflinger/Android.mk
@@ -66,6 +66,13 @@
     LOCAL_CFLAGS += -DVSYNC_EVENT_PHASE_OFFSET_NS=0
 endif
 
+# See build/target/board/generic/BoardConfig.mk for a description of this setting.
+ifneq ($(SF_VSYNC_EVENT_PHASE_OFFSET_NS),)
+    LOCAL_CFLAGS += -DSF_VSYNC_EVENT_PHASE_OFFSET_NS=$(SF_VSYNC_EVENT_PHASE_OFFSET_NS)
+else
+    LOCAL_CFLAGS += -DSF_VSYNC_EVENT_PHASE_OFFSET_NS=0
+endif
+
 ifneq ($(PRESENT_TIME_OFFSET_FROM_VSYNC_NS),)
     LOCAL_CFLAGS += -DPRESENT_TIME_OFFSET_FROM_VSYNC_NS=$(PRESENT_TIME_OFFSET_FROM_VSYNC_NS)
 else