Install Chrome Logger extension from Chrome Store
Install the ChromePHP package, builded package can be found in _packages folder.
Turn on Chrome Logger (blue icon indicates that Chrome Logger is turned on).
Start logging.
$this->modx->chromephp->log('Test log');
$this->modx->chromephp->warn('Test warn');
$this->modx->chromephp->error('Test error');
$this->modx->chromephp->group('Group');
$this->modx->chromephp->log('Log in group', ' Next log in group');
$this->modx->chromephp->warn($this->modx->getObject('modResource', 1));
$this->modx->chromephp->groupEnd();
$this->modx->chromephp->groupCollapsed('Collapsed group');
$this->modx->chromephp->log('Log in collapsed group');
$this->modx->chromephp->groupEnd();