Added benchmark for descendant-or-self

benchmark/xpath/evaluator/descendant_or_self_bench.rb

@@ -0,0 +1,13 @@
+require_relative '../../benchmark_helper'
+
+document = Oga.parse_html(read_html)
+
+Benchmark.ips do |bench|
+  bench.report 'short form' do
+    document.xpath('//meta')
+  end
+
+  bench.report 'long form' do
+    document.xpath('descendant-or-self::meta')
+  end
+end