node: set process._eventsCount to 0 on startup

process is an EventEmitter. There are operations that increment and
decrement the _eventsCount property of an EventEmitter.
process._eventsCount would previously get set to NaN. This change makes
process._eventsCount be calculated as expected.

PR-URL: #5208
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/node.js

@@ -12,6 +12,7 @@
 
   function startup() {
     var EventEmitter = NativeModule.require('events');
+    process._eventsCount = 0;
 
     Object.setPrototypeOf(process, Object.create(EventEmitter.prototype, {
       constructor: {

test/parallel/test-process-emit.js

@@ -18,3 +18,5 @@ process.on('SIGPIPE', common.mustCall((data) => {
 process.emit('normal', 'normalData');
 process.emit(sym, 'symbolData');
 process.emit('SIGPIPE', 'signalData');
+
+assert.strictEqual(isNaN(process._eventsCount), false);