Add benchmark. (#127)

src/ftxui/dom/benchmark_test.cpp

@@ -0,0 +1,35 @@
+#include <benchmark/benchmark.h>
+
+#include "ftxui/dom/elements.hpp"  // for separator, gauge, operator|, text, Element, blink, inverted, hbox, vbox, border
+#include "ftxui/dom/node.hpp"      // for Render
+#include "ftxui/screen/box.hpp"    // for ftxui
+#include "ftxui/screen/screen.hpp"  // for Screen
+
+using namespace ftxui;
+
+static void BencharkBasic(benchmark::State& state) {
+  while (state.KeepRunning()) {
+    auto document = vbox({
+                        text(L"Test"),
+                        separator(),
+                        hbox({
+                            gauge(0.9),
+                            separator() | blink,
+                            gauge(0.5),
+                            separator() | inverted,
+                            gauge(0.1),
+                            separator(),
+                        }),
+                        text(L"Test"),
+                    }) |
+                    border;
+    auto root = gauge(1.0);
+    Screen screen(80, state.range(0));
+    Render(screen, root);
+  }
+}
+BENCHMARK(BencharkBasic)->DenseRange(0, 256, 16);
+
+// Copyright 2021 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.l