It might be helpful to have a book to read while you wait for the source code tree to sync for the first time. The whole thing amounts to around 2.4GB of code, including all the various layout tests used to debug the WebKit rendering engine. Google says the entire download should take about an hour, depending on network activity. In my case it took at least twice that long, despite a 6Mbit broadband connection.

Dissecting a browser

Examination of the source tree reveals some interesting tidbits. Except in cases where code was borrowed from other projects, the source is released under a three-clause BSD-style license, one of the most permissive open source licenses. Google clearly has no qualms about Chromium code being used in commercial settings.

When Chromium does borrow, it's mostly from the expected sources. Besides the WebKit HTML rendering engine, the tree includes the typical libraries for displaying JPEGs, compressing files, and so on. It uses hunspell for its automatic spell-checker -- the same library used by Firefox 3 -- so you can expect that feature to work identically on both browsers.

Overall, the code looks clean and is well organized. Firefox is frequently criticized for its large, Byzantine codebase. By comparison, the Chromium code seems much more accessible to the casual programmer. Comments are plentiful, and they occasionally display some of the humor that makes the best open source projects so much fun. For example, one component of the browser core is a debugging aid dubbed the "jank-o-meter." A comment inside the source explains: "Put break point here if you want to stop threads and look at what caused the jankiness."

Interestingly, Chromium was designed with a certain amount of modularity built in. For example, if for some reason you don't want to use Chromium's ultra-fast V8 JavaScript engine, you can change a few compile-time flags and build it with JavaScriptCore, the engine that ships with WebKit, instead.

What is not immediately evident, however, is any kind of extension mechanism. There is no directory in the source tree called "plug-ins," for example. Building an ad blocker for Chrome might be harder than it sounds.

Putting it all together

Next up: Building the actual browser. To build Chrome for Windows, you'll need Visual Studio 2005 Service Pack 1 (plus some optional patches for improved performance and Vista compatibility) and the current Windows SDK. Neither Visual Studio 2003 nor 2008 are supported currently, due to incompatibility with certain parts of the Chromium codebase.