console: timeEnd() with no label emits warning

When timeEnd() provided with label that doesn't exists
it emits warning in the console, so developer get know about it.

PR-URL: https://github.com/nodejs/node/pull/5901
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

lib/console.js

@@ -67,9 +67,10 @@ Console.prototype.time = function(label) {
 
 
 Console.prototype.timeEnd = function(label) {
-  var time = this._times.get(label);
+  const time = this._times.get(label);
   if (!time) {
-    throw new Error(`No such label: ${label}`);
+    process.emitWarning(`No such label '${label}' for console.timeEnd()`);
+    return;
   }
   const duration = process.hrtime(time);
   const ms = duration[0] * 1000 + duration[1] / 1e6;

test/parallel/test-console.js

@@ -1,6 +1,6 @@
 'use strict';
-require('../common');
-var assert = require('assert');
+const common = require('../common');
+const assert = require('assert');
 
 assert.ok(process.stdout.writable);
 assert.ok(process.stderr.writable);
@@ -8,7 +8,11 @@ assert.ok(process.stderr.writable);
 assert.equal('number', typeof process.stdout.fd);
 assert.equal('number', typeof process.stderr.fd);
 
-assert.throws(function() {
+assert.doesNotThrow(function() {
+  process.once('warning', common.mustCall((warning) => {
+    assert(/no such label/.test(warning.message));
+  }));
+
   console.timeEnd('no such label');
 });