SurfaceFlinger: add a sysprop to control frame rate override

Adding 'ro.surface_flinger.enable_frame_rate_override' to control
whether frame rate override feature should be enabled or not.

Bug: 170502573
Bug: 176940141
Test: atest FrameRateOverrideHostTest
Change-Id: Id7b7a405c6493606af4149d77a4c3d90afc9a5b7
diff --git a/services/surfaceflinger/SurfaceFlingerProperties.h b/services/surfaceflinger/SurfaceFlingerProperties.h
index 37a6b40..816cb09 100644
--- a/services/surfaceflinger/SurfaceFlingerProperties.h
+++ b/services/surfaceflinger/SurfaceFlingerProperties.h
@@ -98,6 +98,8 @@
 
 bool update_device_product_info_on_hotplug_reconnect(bool defaultValue);
 
+bool enable_frame_rate_override(bool defaultValue);
+
 } // namespace sysprop
 } // namespace android
 #endif // SURFACEFLINGERPROPERTIES_H_