Enable mouse wheel autoscroll feature in Chrome
Solution 1:
There's an extension called AutoScroll that enables scrolling while pressing a middle button.
You can also enable it everywhere in OS X with Smart Scroll. See this question.
To make middle clicking work with a Magic Mouse, you'd also need to install an application like BetterTouchTool or MagicPrefs.
Solution 2:
Smooze offers that, among other things. (I'm the developer)
Also, upon releasing the Auto Scroll, the scroll will continue to animate just like the iPhone scroll works. (this of course can be configured or turned off)
