benchmark: util._extend vs object.assign

To copy the values of all enumerable own properties from-
a source object to a target object, node still use-
`util._extend`, though newer standard `Object.assign`
is available. This is because `util._extend` is found to
be faster than `Object.assign`. This benchmark test is
to keep track of how performance compare.
PR-URL: #7255
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

Author: suryagh

benchmark/misc/util-extend-vs-object-assign.js

@@ -0,0 +1,40 @@
+'use strict';
+
+constcommon=require('../common.js');
+constutil=require('util');
+constv8=require('v8');
+
+constbench=common.createBenchmark(main,{
+type: ['extend','assign'],
+n: [10e4]
+});
+
+functionmain(conf){
+letfn;
+constn=conf.n|0;
+letv8command;
+
+if(conf.type==='extend'){
+fn=util._extend;
+v8command='%OptimizeFunctionOnNextCall(util._extend)';
+}elseif(conf.type==='assign'){
+fn=Object.assign;
+// Object.assign is built-in, cannot be optimized
+v8command='';
+}
+
+// Force-optimize the method to test so that the benchmark doesn't
+// get disrupted by the optimizer kicking in halfway through.
+for(vari=0;i<conf.type.length*10;i+=1)
+fn({},process.env);
+
+v8.setFlagsFromString('--allow_natives_syntax');
+eval(v8command);
+
+varobj=newProxy({},{set: function(a,b,c){returntrue;}});
+
+bench.start();
+for(varj=0;j<n;j+=1)
+fn(obj,process.env);
+bench.end(n);
+}