SurfaceFlinger: add debug information when vsync is not generated

Print debug information about VsyncReactor internal state when
we expect a vsync event but it is not generated.

Bug: 151892277
Test: adb shell dumpsys SurfaceFlinger --dispsync
Test: simulate a missed vsync and observed logcat
Change-Id: Ia98cb884321d0c25610c4d721f422d9cd05c8c5e
diff --git a/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.h b/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.h
index fd0a034..390e0c4 100644
--- a/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.h
+++ b/services/surfaceflinger/Scheduler/VSyncDispatchTimerQueue.h
@@ -71,6 +71,8 @@
     // Block calling thread while the callback is executing.
     void ensureNotRunning();
 
+    void dump(std::string& result) const;
+
 private:
     std::string const mName;
     VSyncDispatch::Callback const mCallback;
@@ -86,7 +88,7 @@
     std::optional<ArmingInfo> mArmedInfo;
     std::optional<nsecs_t> mLastDispatchTime;
 
-    std::mutex mRunningMutex;
+    mutable std::mutex mRunningMutex;
     std::condition_variable mCv;
     bool mRunning GUARDED_BY(mRunningMutex) = false;
 };
@@ -112,6 +114,7 @@
     void unregisterCallback(CallbackToken token) final;
     ScheduleResult schedule(CallbackToken token, nsecs_t workDuration, nsecs_t earliestVsync) final;
     CancelResult cancel(CallbackToken token) final;
+    void dump(std::string& result) const final;
 
 private:
     VSyncDispatchTimerQueue(VSyncDispatchTimerQueue const&) = delete;