Implement core_count RPC for Node.JS to track new master version of services.proto and control.proto

src/node/performance/worker_service_impl.js

@@ -33,6 +33,7 @@
 
 'use strict';
 
+var os = require('os');
 var BenchmarkClient = require('./benchmark_client');
 var BenchmarkServer = require('./benchmark_server');
 
@@ -130,3 +131,7 @@ exports.runServer = function runServer(call) {
     });
   });
 };
+
+exports.coreCount = function coreCount(call, callback) {
+  callback(null, {cores: os.cpus().length});
+};