benchmark: add buffer fill benchmark

PR-URL: https://github.com/nodejs/node/pull/18790
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

benchmark/buffers/buffer-fill.js

@@ -0,0 +1,31 @@
+'use strict';
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  type: [
+    'fill(0)',
+    'fill("")',
+    'fill(100)',
+    'fill(400)',
+    'fill("t")',
+    'fill("test")',
+    'fill("t", "utf8")',
+    'fill("t", 0, "utf8")',
+    'fill("t", 0)',
+    'fill(Buffer.alloc(1), 0)'
+  ],
+  size: [2 ** 8, 2 ** 13, 2 ** 16],
+  n: [2e4]
+});
+
+function main({ n, type, size }) {
+  const buffer = Buffer.allocUnsafe(size);
+  const testFunction = new Function('b', `
+    for (var i = 0; i < ${n}; i++) {
+      b.${type || 'fill(0)'};
+    }
+  `);
+  bench.start();
+  testFunction(buffer);
+  bench.end(n);
+}