Add Defer<FnT> type to defer actions to the end of scope.

include/Defer.h

@@ -0,0 +1,18 @@
+#pragma once
+
+#include <functional>
+
+template <typename FnT>
+class Defer final {
+public:
+    Defer(FnT fn)
+        : mFunction([&fn] { (void)fn(); }) { }
+    ~Defer() {
+        if (mFunction) {
+            mFunction();
+        }
+    }
+
+private:
+    std::function<void()> mFunction;
+};