Why Chrome does not show CSS3 ::-webkit-scrollbar scrollbar for iframe?

Demo http://jsfiddle.net/laukstein/C9s3P/

<iframe scrolling="yes" style="overflow-x:hidden; overflow-y:scroll; width:150px; height:50px;" src="http://en.wikipedia.org/wiki/Web_browser"></iframe>

CSS

::-webkit-scrollbar{
    width:0.8em;
    height:0.8em;
    background-color:#fff;
}
::-webkit-scrollbar:hover{
    background-color:#eee;
}
::-webkit-resizer{
    -webkit-border-radius:4px;
    background-color:#666;
}
::-webkit-scrollbar-thumb{
    min-height:0.8em;
    min-width:0.8em;
    -webkit-border-radius:4px;
    background-color: #ddd;
}
::-webkit-scrollbar-thumb:hover{
    background-color: #bbb;
}
::-webkit-scrollbar-thumb:active{
    background-color:#888;
}