[Magneto]

Навскидку:

<style>
* {
  margin: 0;
  padding: 0;
  border: 0;
}

body, html {
  height: 100%
}

#wrapper {
  border-bottom: solid 150px transparent;
  position: absolute;
  top: 0px;
  left: 0px;
  bottom: 0px;
  right: 0px;
}

#top {
  width: 100%;
  height: 100%;
}

#bottom {
  width: 100%;
  height: 150px;
  position: absolute;
  bottom: 0px;
}
</style>

<div id="wrapper">
  <iframe id="top" src="http://habrahabr.ru"></iframe>
</div>
  <iframe id="bottom" src="http://javascript.ru"></iframe>