bench: add merkle bench.

bench/merkle.js

@@ -0,0 +1,22 @@
+'use strict';
+
+const assert = require('assert');
+const merkle = require('../lib/crypto/merkle');
+const random = require('../lib/crypto/random');
+const bench = require('./bench');
+
+const leaves = [];
+
+for (let i = 0; i < 3000; i++)
+  leaves.push(random.randomBytes(32));
+
+{
+  let end = bench('tree');
+  let i;
+  for (i = 0; i < 1000; i++) {
+    let [n, m] = merkle.createTree(leaves.slice());
+    assert(n);
+    assert(!m);
+  }
+  end(i);
+}