Apple - Enable mouse wheel autoscroll feature in Chrome

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.

Smooze offers that, among other things. (I'm the developer)

What differentiate it from other cross platform suggestions is the ability to use it in every mac app while still identify links, for example. (in case you use your middle button drag to grab and throw but still want that a middle button click will act as a middle button)

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)