code: function(obj, callback) {
        if (!obj.trace) {
          var errorMsg = "Trace objects must contain the property 'trace'";
          this.logger(errorMsg);
          if (callback) {
            callback(new Error(errorMsg));
          }
          return;
        }
  
        var item = {body: {trace: obj.trace}};
        if (callback) {
          item.callback = callback;
        }
  
        // merge other props as top-level
        for (var k in obj) {
          if (k !== 'trace' && k !== '_t') {
            item[k] = obj[k];
          }
        }
  
        this.items.push(item);
        this.handleEvents();
      }
docs: /*
  Reports raw trace objects. This is used for building enhanced or modified stack traces.
  
  var trace = {
  exception: {'class': 'TypeError', 'message': 'blah'},
  frames: [{filename: 'http://example.com/script.js', method: 'doSomething', lineno: 55}, ...]
  }
  
  To call via _rollbar.push():
  _rollbar.push({_t: 'trace', trace: trace});