Timer + IFrameHeightResizer + BaconIpsum: http://plnkr.co/edit/lcpbkXBe1faNsgUu2nUQ?p=preview

IFrameHeightResizer.js

/*
 * Timer
 */
function Timer(callback, interval) {
  this.nextTick = window.requestAnimationFrame || window.setTimeout;
  this.interval = interval || 50;
  this.callback = callback;
}

Timer.prototype.start = function() {
  var self = this;
  // Use setTimeout for adjusting frame rate.
  // http://creativejs.com/resources/requestanimationframe/
  this.timer = setTimeout(function() {
    self.start();
    self.callback && self.callback();
  }, this.interval);
  
  return this;
}; 

Timer.prototype.stop = function() {
  clearTimeout(this.timer);
  
  return this;
};

/*
 * IFrameHeightResizer
 */
function IFrameHeightResizer(iframe) {
  this.iframe = iframe;
  this.oldHeight = 0;
  this.timer = new Timer(this.check.bind(this)).start();
  
  this.check();
}

IFrameHeightResizer.prototype.check = function() {
  // https://developer.mozilla.org/en-US/docs/Web/API/CSS_Object_Model/Determining_the_dimensions_of_elements
  var newHeight = this.iframe.contentWindow.document.body.scrollHeight;
  
  if (newHeight !== this.oldHeight) {
    this.adjust(newHeight);
  }
};

IFrameHeightResizer.prototype.adjust = function(newHeight) {
  console.log('adjust from %d to %d', this.oldHeight, newHeight);
  this.oldHeight = newHeight;
  this.iframe.style.height = this.oldHeight + 'px';
};

/*
 * BaconIpsum
 */
function BaconIpsum(iframe) {
  this.iframe = iframe;
  this.url = 'http://baconipsum.com/api/?callback=?';
  this.params = { 
	  type: 'meat-and-filler', 
	  paras: 3 
	};
	
  new Timer(this.fetch.bind(this), 5000).start();
}

BaconIpsum.prototype.fetch = function() {
  var self = this;
  this.params.paras = Math.floor(Math.random() * 10) + 1;
      
  $.getJSON(this.url, this.params).then(function(data) {
    console.log('fetch', data);
    self.iframe.contentWindow.document.body.innerHTML = data.join();
  });
};

// Start
document.addEventListener('DOMContentLoaded', function() {
  var iframe = document.querySelector('iframe');
   
  // Check contents in iframe
  new IFrameHeightResizer(iframe);
  
  // Get BaconIpsum text each 5 sec.
  new BaconIpsum(iframe);
});