SF: add a spinner to refresh rate overlay

Add a spinner to refresh rate overlay to visualize when the
display updates.

Test: adb shell setprop sf.debug.show_refresh_rate_overlay_spinner 1
and enable refresh rate overlay

Change-Id: I089df8437cffb45ef631772fe0179970f21abfa0
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 7ab0729..d56321d 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -547,6 +547,8 @@
     bool mKernelIdleTimerEnabled = false;
     // Keeps track of whether the kernel timer is supported on the SF side.
     bool mSupportKernelIdleTimer = false;
+    // Show spinner with refresh rate overlay
+    bool mRefreshRateOverlaySpinner = false;
     /* ------------------------------------------------------------------------
      * Message handling
      */