Add a flag to control the VRR hint for timeout

Only disables the hint for timeout.

Test: tested with sys prop enabled and disabled
adb shell setprop debug.sf.vrr_timeout_hint_enabled false
adb shell setprop debug.sf.vrr_timeout_hint_enabled true

BUG: 316615878
Change-Id: I678dfa018f7568bae96b82238e3466776e009ba6
diff --git a/services/surfaceflinger/DisplayHardware/HWComposer.h b/services/surfaceflinger/DisplayHardware/HWComposer.h
index 4ca528a..fb32ff4 100644
--- a/services/surfaceflinger/DisplayHardware/HWComposer.h
+++ b/services/surfaceflinger/DisplayHardware/HWComposer.h
@@ -491,6 +491,7 @@
 private:
     // For unit tests
     friend TestableSurfaceFlinger;
+    friend HWComposerTest;
 
     struct DisplayData {
         std::unique_ptr<HWC2::Display> hwcDisplay;
@@ -542,6 +543,7 @@
 
     const size_t mMaxVirtualDisplayDimension;
     const bool mUpdateDeviceProductInfoOnHotplugReconnect;
+    bool mEnableVrrTimeout;
 };
 
 } // namespace impl