SurfaceFlinger: fix SFFakeHWC_test

Few small fixes to make the test pass.

Fixes: 147250281
Test: adb shell data/nativetest64/sffakehwc_test/sffakehwc_test
Change-Id: I1e2ef20adcdd10a78b621eb1bea21a2d30c22afe
diff --git a/services/surfaceflinger/Scheduler/PhaseOffsets.h b/services/surfaceflinger/Scheduler/PhaseOffsets.h
index 7b1bdfd..b7d4eae 100644
--- a/services/surfaceflinger/Scheduler/PhaseOffsets.h
+++ b/services/surfaceflinger/Scheduler/PhaseOffsets.h
@@ -108,6 +108,7 @@
 
 private:
     std::unordered_map<float, Offsets> initializeOffsets(const std::vector<float>&) const;
+    PhaseDurations::Offsets constructOffsets(nsecs_t vsyncDuration) const;
 
     const nsecs_t mSfDuration;
     const nsecs_t mAppDuration;