NVFlinger: Lock race condition between CPU, Host Timing, VSync.

src/core/hle/service/nvflinger/nvflinger.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include <memory>
+#include <mutex>
 #include <optional>
 #include <string>
 #include <string_view>
@@ -79,6 +80,10 @@ public:
 
     s64 GetNextTicks() const;
 
+    std::unique_lock<std::mutex> Lock() {
+        return std::unique_lock{*guard};
+    }
+
 private:
     /// Finds the display identified by the specified ID.
     VI::Display* FindDisplay(u64 display_id);
@@ -108,6 +113,8 @@ private:
     /// Event that handles screen composition.
     std::shared_ptr<Core::Timing::EventType> composition_event;
 
+    std::shared_ptr<std::mutex> guard;
+
     Core::System& system;
 };