Add unit test on sending power hints in SurfaceFlinger

Bug: b/204322192
Test: atest libsurfaceflinger_unittest:libsurfaceflinger_unittest.SurfaceFlingerPowerHintTest#sendDurationsIncludingHwcWaitTime
Change-Id: I0c9ba1abc169ba0b2136663e3937cd93191730ae
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 910c5bb..07da731 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -1383,7 +1383,7 @@
     sp<os::IInputFlinger> mInputFlinger;
     InputWindowCommands mInputWindowCommands;
 
-    Hwc2::impl::PowerAdvisor mPowerAdvisor;
+    std::unique_ptr<Hwc2::PowerAdvisor> mPowerAdvisor;
 
     void enableRefreshRateOverlay(bool enable) REQUIRES(mStateLock);