code: function _addLoadHandler(frame) {
              var load = function() {
                  this.loading = false;
  
                  if (this.handshakeAttempts === this.handshakeAttemptsOrig) {
                      // Probably a first try for handshake or a reload of the iframe,
                      // Either way, we'll need to perform handshake, so ready flag should be set to false (if not already)
                      this.ready = false;
                  }
  
                  _handshake.call(this, this.handshakeInterval);
              }.bind(this);
  
              PostMessageUtilities.addEventListener(frame, "load", load);
  
              return function() {
                  _removeLoadHandler(frame, load);
              };
          }
docs: Add load handler for the iframe to make sure it is loaded
  @param {Object} frame - the actual DOM iframe
  @returns {Function} the remove handler function
  @private