code: function metrics(obj, data) {
    var dimensions = data.dimensions;
    var metrics = data.metrics;
    var names = keys(metrics).concat(keys(dimensions));
    var ret = {};
  
    for (var i = 0; i < names.length; ++i) {
      var name = names[i];
      var key = metrics[name] || dimensions[name];
      var value = dot(obj, name) || obj[name];
      if (value == null) continue;
      ret[key] = value;
    }
  
    return ret;
  }
docs: Map google's custom dimensions & metrics with `obj`.
  
  Example:
  
  metrics({ revenue: 1.9 }, { { metrics : { revenue: 'metric8' } });
  // => { metric8: 1.9 }
  
  metrics({ revenue: 1.9 }, {});
  // => {}
  
  @param {Object} obj
  @param {Object} data
  @return {Object|null}
  @api private