Add option for reporting launcher stdout/stderr in Karma log

[binji]

See https://github.com/karma-runner/karma/issues/1199

I am using Karma to run Native Client, which by default outputs to Chrome stdout/stderr. I'd like to redirect this output the karma log. I have a hack that does this:

var self = this;
var log = logger.create('Chrome stderr');
var oldStart = this._start;

this._start = function(url) {
  oldStart(url);

  var prevStderr = '';
  self._process.stderr.on('data', function(data) {
    var msg = prevStderr + data.toString();
    var start = 0;
    while (true) {
      var end = msg.indexOf('\n', start);
      if (end !== -1) {
        log.info(msg.slice(start, end));
        start = end + 1;
      } else {
        prevStderr = msg.slice(start);
        break;
      }
    }
  });

Is this reasonable to add? Is there a better way to do this?

[dignifiedquire]

Sounds reasonable to add. If you want make PR including an option to enable this, and having it disabled by default. Plus some small documentation on how to use it. Thanks

[ogonkov]

https://github.com/CodeYellowBV/run-headless-chromium already run headless chrome w/ stdout output (but replacing CHROME_BIN seems didn't work for me)