SurfaceFlinger: add logging when changing refresh rate policy

Add a log message when refresh rate policy is changed to help
debug issues when SF changes refresh rate unexpectedly.

Bug: 230590870
Test: change policy over adb and observe logs
Change-Id: I31cdc3ad47ea25c0f700ebad897e7efbc986bd24
diff --git a/services/surfaceflinger/DisplayDevice.h b/services/surfaceflinger/DisplayDevice.h
index d5d87b4..2161436 100644
--- a/services/surfaceflinger/DisplayDevice.h
+++ b/services/surfaceflinger/DisplayDevice.h
@@ -249,6 +249,10 @@
     nsecs_t getVsyncPeriodFromHWC() const;
     nsecs_t getRefreshTimestamp() const;
 
+    status_t setRefreshRatePolicy(
+            const std::optional<scheduler::RefreshRateConfigs::Policy>& policy,
+            bool overridePolicy);
+
     // release HWC resources (if any) for removable displays
     void disconnect();
 
@@ -303,6 +307,8 @@
     TracedOrdinal<bool> mDesiredActiveModeChanged
             GUARDED_BY(mActiveModeLock) = {"DesiredActiveModeChanged", false};
     ActiveModeInfo mUpcomingActiveMode GUARDED_BY(kMainThreadContext);
+
+    std::atomic_int mNumModeSwitchesInPolicy = 0;
 };
 
 struct DisplayDeviceState {