Add a benchmark about using JS Symbols vs Strings

Author: elia

benchmark-ips/bm_js_symbols_vs_strings.rb

@@ -0,0 +1,28 @@
+Benchmark.ips do |x|
+  %x{
+    var o = {}
+    o[Symbol.for('foo')] = 123
+    o.foo = 123
+    var foo = Symbol('foo')
+    o[foo] = 123
+    var a = 0, b = 0, c = 0
+  }
+
+  x.report('global symbol') do
+    `a += o[Symbol.for('foo')]`
+  end
+
+  x.report('symbol') do
+    `a += o[foo]`
+  end
+
+  x.report('ident') do
+    `b += o.foo`
+  end
+
+  x.report('string') do
+    `c += o['foo']`
+  end
+
+  x.compare!
+end