add benchmark util

script/benchmark.dart

@@ -0,0 +1,55 @@
+import 'package:xterm/xterm.dart';
+
+void main() {
+  BenchmarkWrite().run();
+  BenchmarkWriteBuffer().run();
+}
+
+abstract class Benchmark {
+  String explain();
+
+  void benchmark();
+
+  void run() {
+    print('benchmark: ${explain()}');
+    print('preheating...');
+    benchmark();
+    final sw = Stopwatch()..start();
+    print('running...');
+    benchmark();
+    sw.stop();
+    print('result: ${sw.elapsedMilliseconds} ms');
+  }
+}
+
+class BenchmarkWrite extends Benchmark {
+  static const cycle = 1 << 20;
+  static const data = 'hello world';
+
+  String explain() {
+    return "write '$data' to Terminal for $cycle times";
+  }
+
+  void benchmark() {
+    final terminal = Terminal();
+    for (var i = 0; i < cycle; i++) {
+      terminal.write(data);
+    }
+  }
+}
+
+class BenchmarkWriteBuffer extends Benchmark {
+  static const cycle = 1 << 20;
+  static const data = 'hello world';
+
+  String explain() {
+    return "write '$data' to StringBuffer for $cycle times";
+  }
+
+  void benchmark() {
+    final buffer = StringBuffer();
+    for (var i = 0; i < cycle; i++) {
+      buffer.write(data);
+    }
+  }
+}